Kurt Nørmark ©
Department of Computer Science, Aalborg University, Denmark

Abstract Previous lecture Next lecture Index References Contents

In this lecture we will introduce the programming language C#. Recall that we assume that the reader has experience with C, or at least a similar imperative language. In the central part of this lecture we will address how C# differs from C. This is done by 'a tour through C' in which we explain the major similarities and differences between the two languages.

C# has been inspired by earlier object-oriented programming languages

Simula (1967) The very first object-oriented programming language C++ (1983) The first object-oriented programming language in the C family of languages Java (1995) Sun's object-oriented programming language C# (2001) Microsoft's object-oriented programming language

Reference Computer Language History

The Common Language Infrastructure Slide Annotated slide Contents Index References Textbook

The Common Language Infrastructure (CLI) is a specification that allows several different programming languages to be used together on a given platform

Parts of the Common Language Infrastructure: Common Intermediate language (CIL) including a common type system (CTS) Common Language Specification (CLS) - shared by all languages Virtual Execution System (VES) Metadata about types, dependent libraries, attributes, and more

MONO and .NET are both implementations of the Common Language Infrastructure The C# language and the Common Language Infrastructure are standardized by ECMA and ISO

CLI Overview from Wikipedia Slide Annotated slide Contents Index References Textbook

Figure. Wikipedia's overview diagram of the CLI

C# Compilation and Execution Slide Annotated slide Contents Index References Textbook

The Common Language Infrastructure supports a two-step compilation process

Compilation The C# compiler: Translation of C# source to CIL Produces .dll and .exe files Just in time compilation: Translation of CIL to machine code Execution With interleaved Just in Time compilation On Mono: Explicit activation of the interpreter On Window: Transparent activation of the interpreter

.dll and .exe files are - with some limitations - portable in between different platforms

Most simple types in C# are similar to the simple types in C

Major differences: All simple C# types have fixed bit sizes C# has a boolean type called bool C# chars are 16 bit long In C# there is a high-precision 128 bit numeric fixed-point type called decimal Pointers are not supported in the normal parts of a C# program In the unsafe part C# allows for pointers like in C All simple types are in reality structs in C#, and therefore they have members Differences compared to C.

Program: Demonstrations of the simple type bool in C#. Shows boolean constants and how to deal with the default boolean value (false).

using System; class BoolDemo{ public static void Main(){ bool b1, b2; b1 = true; b2 = default(bool); Console.WriteLine("The value of b2 is {0}", b2); // False } }

Program: Demonstrations of the simple type char in C#. Illustrates character constants, hexadecimal escape notation, and character methods.

using System; class CharDemo{ public static void Main(){ char ch1 = 'A', ch2 = '\u0041', ch3 = '\u00c6', ch4 = '\u00d8', ch5 = '\u00c5', ch6; Console.WriteLine("ch1 is a letter: {0}", char.IsLetter(ch1)); Console.WriteLine("{0} {1} {2}", ch3, ch4, char.ToLower(ch5)); ch6 = char.Parse("B"); Console.WriteLine("{0} {1}", char.GetNumericValue('3'), char.GetNumericValue('a')); } }

Program: Demonstrations of numeric types in C#. Illustrates all numeric types in C#. Exercises minimum and maximum values of the numeric types.

using System; using System.Globalization; class NumberDemo{ public static void Main(){ sbyte sb1 = sbyte.MinValue; // Signed 8 bit integer System.SByte sb2 = System.SByte.MaxValue; Console.WriteLine("sbyte: {0} : {1}", sb1, sb2); byte b1 = byte.MinValue; // Unsigned 8 bit integer System.Byte b2 = System.Byte.MaxValue; Console.WriteLine("byte: {0} : {1}", b1, b2); short s1 = short.MinValue; // Signed 16 bit integer System.Int16 s2 = System.Int16.MaxValue; Console.WriteLine("short: {0} : {1}", s1, s2); ushort us1 = ushort.MinValue; // Unsigned 16 bit integer System.UInt16 us2= System.UInt16.MaxValue; Console.WriteLine("ushort: {0} : {1}", us1, us2); int i1 = int.MinValue; // Signed 32 bit integer System.Int32 i2 = System.Int32.MaxValue; Console.WriteLine("int: {0} : {1}", i1, i2); uint ui1 = uint.MinValue; // Unsigned 32 bit integer System.UInt32 ui2= System.UInt32.MaxValue; Console.WriteLine("uint: {0} : {1}", ui1, ui2); long l1 = long.MinValue; // Signed 64 bit integer System.Int64 l2 = System.Int64.MaxValue; Console.WriteLine("long: {0} : {1}", l1, l2); ulong ul1 = ulong.MinValue; // Unsigned 64 bit integer System.UInt64 ul2= System.UInt64.MaxValue; Console.WriteLine("ulong: {0} : {1}", ul1, ul2); float f1 = float.MinValue; // 32 bit floating-point System.Single f2= System.Single.MaxValue; Console.WriteLine("float: {0} : {1}", f1, f2); double d1 = double.MinValue; // 64 bit floating-point System.Double d2= System.Double.MaxValue; Console.WriteLine("double: {0} : {1}", d1, d2); decimal dm1 = decimal.MinValue; // 128 bit fixed-point System.Decimal dm2= System.Decimal.MaxValue; Console.WriteLine("decimal: {0} : {1}", dm1, dm2); string s = sb1.ToString(), t = 123.ToString(); } }

Program: Output from the numeric demo program. Output from the program above. Reveals minimum and maximum values of all the numeric types.

sbyte: -128 : 127 byte: 0 : 255 short: -32768 : 32767 ushort: 0 : 65535 int: -2147483648 : 2147483647 uint: 0 : 4294967295 long: -9223372036854775808 : 9223372036854775807 ulong: 0 : 18446744073709551615 float: -3,402823E+38 : 3,402823E+38 double: -1,79769313486232E+308 : 1,79769313486232E+308 decimal: -79228162514264337593543950335 : 79228162514264337593543950335

Exercise 2.3. Exploring the type Char

The type System.Char (a struct) contains a number of useful methods, and a couple of constants. Locate the type System.Char in your C# documentation and take a look at the methods available on characters. You may ask where you find the C# documentation. There are several possibilities. You can find it at the Microsoft MSDN web site at msdn.microsoft.com. It is also integrated in Visual Studio and - to some degree - in Visual C# express. It comes with the C# SDK, as a separate browser. It is also part of the documentation web pages that comes with Mono. If you are a Windows user I will recommend the Windows SDK Documentation Browser which is bundled with the C# SDK. Along the line of the character demo program above, write a small C# program that uses the char predicates IsDigit, IsPunctuation, and IsSeparator. It may be useful to find the code position - also known as the code point - of a character. As an example, the code position of 'A' is 65. Is there a method in System.Char which gives access to this information? If not, can you find another way to find the code position of a character? Be sure to understand the semantics (meaning) of the method GetNumericValue in type Char.

Exercise 2.3. Hexadecimal numbers

In this exercise we will write a program that can convert between decimal and hexadecimal notation of numbers. Please consult the focus boxes about hexadecimal numbers in the text book version if you need to. You might expect that this functionality is already present in the C# libraries. And to some degree, it is. The static method ToInt32(string, Int32) in class Convert converts the string representation of a number (the first parameter) to an arbitrary number system (the second parameter). Similar methods exist for other integer types. The method ToString(string) in the struct Int32, can be used for conversion from an integer to a hexadecimal number, represented as a string. The parameter of ToString is a format string. If you pass the string "X" you get a hexadecimal number. The program below shows examples: using System; class NumberDemo{ public static void Main(){ int i = Convert.ToInt32("7B", 16); // hexadecimal 7B (in base 16) -> // decimal 123 Console.WriteLine(i); // 123 Console.WriteLine(123.ToString("X")); // decimal 123 -> hexadecimal 7B } } Now, write a method which converts a list (or array) of digits in base 16 (or more generally, base b, b >= 2) to a decimal number. The other way around, write a method which converts a positive decimal integer to a list (or array) of digits in base 16 (or more generally, base b). Here is an example where the requested methods are used: public static void Main(){ int r = BaseBToDecimal(16, new List{7, 11}); // 7B -> 123 List s = DecimalToBaseB(16, 123); // 123 -> {7, 11} = 7B List t = DecimalToBaseB(2, 123); // 123 -> {1, 1, 1, 1, 0, 1, 1 } = // 1111011 Console.WriteLine(r); foreach (int digit in s) Console.Write("{0} ", digit); Console.WriteLine(); foreach (int digit in t) Console.Write("{0} ", digit); }

References The struct System.Char Decimal Floating Point in .NET The struct System.Sbyte The struct System.Byte The struct System.Int16 The struct System.UInt16 The struct System.Int32 The struct System.UInt32 The struct System.Int64 The struct System.UInt64 The struct System.Single The struct System.Double The struct System.Decimal

Enumerations types Slide Annotated slide Contents Index References Textbook

Enumeration types provide for symbolic names of selected integer values. Use of enumeration types improves the readability of your programs.

Enumeration types are similar to each other in C and C#

Program: Two examples of enumeration types in C#.

public enum Ranking {Bad, OK, Good} public enum OnOff: byte{ On = 1, Off = 0}

An extension of C enumeration types: Enumeration types of several different underlying types can be defined (not just int) Enumeration types inherit a number of methods from the type System.Enum The symbolic enumeration constants can be printed (not just the underlying number) Values, for which no enumeration constant exist, can be dealt with Combined enumerations represent a collection of enumerations

Program: Demonstration of enumeration types in C#. Programming with Ranking and OnOff.

using System; class NonSimpleTypeDemo{ public enum Ranking {Bad, OK, Good} public enum OnOff: byte{ On = 1, Off = 0} public static void Main(){ OnOff status = OnOff.On; Console.WriteLine(); Console.WriteLine("Status is {0}", status); Ranking r = Ranking.OK; Console.WriteLine("Ranking is {0}", r ); Console.WriteLine("Ranking is {0}", r+1); Console.WriteLine("Ranking is {0}", r+2); bool res1 = Enum.IsDefined(typeof(Ranking), 3); Console.WriteLine("{0} defined: {1}", 3, res1); bool res2= Enum.IsDefined(typeof(Ranking), Ranking.Good); Console.WriteLine("{0} defined: {1}", Ranking.Good , res2); bool res3= Enum.IsDefined(typeof(Ranking), 2); Console.WriteLine("{0} defined: {1}", 2 , res3); foreach(string s in Enum.GetNames(typeof(Ranking))) Console.WriteLine(s); } }

Program: Output from the program that demonstrates enumeration types.

Status is On Ranking is OK Ranking is Good Ranking is 3 3 defined: False Good defined: True 2 defined: True Bad OK Good

Exercise 2.5. ECTS Grades

Define an enumeration type ECTSGrade of the grades A, B, C, D, E, Fx and F and associate the Danish 7-step grades 12, 10, 7, 4, 2, 0, and -3 to the symbolic ECTS grades. What is the most natural underlying type of ECTSGrade? Write a small program which illustrates how to use the new enumeration type.

Exercise 2.5. Use of Enumeration types

Consult the documentation of type type System.Enum, and get a general overview of the methods in this struct. Be sure that you are able to find the documentation of System.Enum Test drive the example EnumTest, which is part of MicroSoft's documentation. Be sure to understand the program relative to its output. Write your own program with a simple enumeration type. Use the Enum.CompareTo method to compare two of the values of your enumeration type.

Non-simple types Slide Annotated slide Contents Index References Textbook

This is about arrays, strings, structs. All the classes and structs that we program ourselves also count as non-simple types.

C# allows for a variety of non-simple types, most important Classes

Similarities Arrays in C#: Indexed from 0. Jagged arrays - arrays of arrays Strings in C#: Same notation as in C, and similar escape characters Structs in C#: A value type like in C.

Differences Arrays: Rectangular arrays in C# Strings: No \0 termination in C# Structs: Much expanded in C#. Structs can have methods.

New kinds of non-simple types in C#: Classes Interfaces Delegates

As an object-oriented programming language, C# is much stronger than C when it comes to definition of our own non-simple types

Reference System.Enum

Arrays and Strings Slide Annotated slide Contents Index References Textbook

Both arrays and strings are classical types, supported by almost any programming language. Both arrays and strings are reference types. It means that arrays and strings are accessed via references.

Both arrays and strings are dealt with as objects in C# In addition, there is special notation in the C# language of arrays and strings

Similarities C# and C have similar syntaxes for arrays and strings

Differences Arrays in C# can be rectangular or jagged (arrays of arrays) In C#, an array is not a pointer to the first element Index out of bound checking is done in C# Strings are immutable in C#, but not in C In C# there are two kinds of string literals: "a string\n" and @"a string\n"

Program: Demonstrations of array types in C#.

using System; class ArrayStringDemo{ public static void Main(){ string[] a1, a2 = {"a", "bb", "ccc"}; a1 = new string[]{"ccc", "bb", "a"}; int[,] b1 = new int[2,4], b2 = {{1,2,3,4}, {5,6,7,8}}; double[][] c1 = { new double[]{1.1, 2.2}, new double[]{3.3, 4.4, 5.5, 6.6} }; Console.WriteLine("Array lengths. a1:{0} b2:{1} c1:{2}", a1.Length, b2.Length, c1.Length); Array.Clear(a2,0,3); Array.Resize<string>(ref a2,10); Console.WriteLine("Lenght of a2: {0}", a2.Length); Console.WriteLine("Sorting a1:"); Array.Sort(a1); foreach(string str in a1) Console.WriteLine(str); } }

Program: Output from the array demonstration program.

Array lengths. a1:3 b2:8 c1:2 Lenght of a2: 10 Sorting a1: a bb ccc

Program: A demonstration of strings in C#.

using System; class ArrayStringDemo{ public static void Main(){ string s1 = "OOP"; System.String s2 = "\u004f\u004f\u0050"; // equivalent Console.WriteLine("s1 and s2: {0} {1}", s1, s2); string s3 = @"OOP on the \n semester ""Dat1/Inf1/SW3"""; Console.WriteLine("\n{0}", s3); string s4 = "OOP on \n the \\n semester \"Dat1/Inf1/SW3\""; Console.WriteLine("\n{0}", s4); string s5 = "OOP E06".Substring(0,3); Console.WriteLine("The substring is: {0}", s5); } }

Program: Output from the string demonstration program.

s1 and s2: OOP OOP OOP on the \n semester "Dat1/Inf1/SW3" OOP on the \n semester "Dat1/Inf1/SW3" The substring is: OOP

Exercise 2.7. Use of array types

Based on the inspiration from the accompanying example, you are in this exercise supposed to experiment with some simple C# arrays. First, consult the documentation of the class System.Array. Please notice the properties and methods that are available on arrays in C#. Declare, initialize, and print an array of names (e.g. array of strings) of all members of your group. Sort the array, and search for a given name using System.Array.BinarySearch method. Reverse the array, and make sure that the reversing works.

Exercise 2.7. Use of string types

Based on the inspiration from the accompanying example, you are in this exercise supposed to experiment with some simple C# strings. First, consult the documentation of the class System.String - either in your documentation browser or at msdn.microsoft.com. Read the introduction (remarks) to string which contains useful information! There exists a large variety of operations on strings. Please make sure that you are aware of these. Many of them will help you a lot in the future! Make a string of your own first name, written with escaped Unicode characters (like we did for "OOP" in the accompanying example). If necessary, consult the unicode code charts (Basic Latin and Latin-1) to find the appropriate characters. Take a look at the System.String.Insert method. Use this method to insert your last name in the first name string. Make your own observations about Insert relative to the fact that strings in C# are immutable.

In C# it is often more attractive to use a (type parameterized) collection class instead of an array

References System.Array System.String

Pointers and references Slide Annotated slide Contents Index References Textbook

References are important in C#. A reference is similar to a point in C, but references are much easier to work with. References can be passed around (via parameters). Objects are always accessed via references, but in contrast to C, the following of a references happens implicitly, and automatically.

References in C# can be understood as a very restricted notion of pointers, as known from C programming

Pointers In normal C# programs: Pointers are not used All the complexity of pointers, pointer arithmetic, dereferencing, and the address operator is not found in normal C# programs In specially marked unsafe sections: Pointers can be used almost as in C. Do not use them in your C# programs! References Objects (instance of classes) are always accessed via references in C# References are automatically dereferenced in C# There are no particular operators in C# that are related to references

Program: Demonstrations of references in C#.

using System; public class C { public double x, y; } public class ReferenceDemo { public static void Main(){ C cRef, anotherCRef; cRef = null; Console.WriteLine("Is cRef null: {0}", cRef == null); cRef = new C(); Console.WriteLine("Is cRef null: {0}", cRef == null); Console.WriteLine("x and y are ({0},{1})", cRef.x, cRef.y); anotherCRef = F(cRef); } public static C F(C p){ Console.WriteLine("x and y are ({0},{1})", p.x, p.y); return p; } }

Program: Output from the reference demo program.

Is cRef null: True Is cRef null: False x and y are (0,0) x and y are (0,0)

There is no particular complexity in normal C# programs due to use of references

Structs Slide Annotated slide Contents Index References Textbook

Structs in C and C# are similar to each other. But structs in C# are extended in several ways compared to C.

The concept of structs has been much extended in C#

Similarities Structs in C# can be used almost in the same way as structs in C Structs are value types in both C and C# Differences Structs in C# are almost as powerful as classes Structs in C# can have operations (methods) in the same way as classes Structs in C# cannot inherit from other structs or classes

Program: Demonstrations of structs in C#.

using System; public struct Point { public double x, y; public Point(double x, double y){this.x = x; this.y = y;} public void Mirror(){x = -x; y = -y;} } // end Point public class StructDemo{ public static void Main(){ Point p1 = new Point(3.0, 4.0), p2; p2 = p1; p2.Mirror(); Console.WriteLine("Point is: ({0},{1})", p2.x, p2.y); } }

Program: Output from the struct demo program.

Point is: (-3,-4)

Program: An extended demonstration of structs in C#.

/* Right, Wrong */ using System; public struct Point1 { public double x, y; } public struct Point2 { public double x, y; public Point2(double x, double y){this.x = x; this.y = y;} public void Mirror(){x = -x; y = -y;} } public class StructDemo{ public static void Main(){ /* Point1 p1; Console.WriteLine(p1.x, p1.y); */ Point1 p2; p2.x = 1.0; p2.y = 2.0; Console.WriteLine("Point is: ({0},{1})", p2.x, p2.y); Point1 p3; p3 = p2; Console.WriteLine("Point is: ({0},{1})", p3.x, p3.y); Point2 p4 = new Point2(3.0, 4.0); p4.Mirror(); Console.WriteLine("Point is: ({0},{1})", p4.x, p4.y); } }

Operators Slide Annotated slide Contents Index References Textbook

This pages shows an overview of all operators in C#.

Most operators in C are also found in C#

Table. The operator priority table of C#. Operators with high level numbers have high priorities. In a given expression, operators of high priority are evaluated before operators with lower priority. The associativity tells if operators at the same level are evaluated from left to right or from right to left.

Level Category Operators Associativity (binary/tertiary) 14 Primary x.y      f(x)      a[x]      x++      x--      new      typeof      checked      unchecked      default      delegate left to right 13 Unary +      -      !      ~      ++x      --x      (T)x      true      false      sizeof left to right 12 Multiplicative *      /      % left to right 11 Additive +      - left to right 10 Shift <<      >> left to right 9 Relational and Type testing <      <=      >      >=      is      as left to right 8 Equality ==      != left to right 7 Logical/bitwise and & left to right 6 Logical/bitwise xor ^ left to right 5 Logical/bitwise or | left to right 4 Conditional and && left to right 3 Conditional or || left to right 2 Null coalescing ?? left to right 1 Conditional ?: right to left 0 Assignment or Lambda expression =      *=      /=      %=      +=      -=      <<=      >>=      &=      ^=      |=      => right to left

Reference Similar table for C

It is possible to overload many of the C# operators This allows for terse and convenient notation in many classes

Commands and Control Structures Slide Annotated slide Contents Index References Textbook

On this page we discuss control structures for selection and iteration. As usual, we concentrate on the differences between C an C#.

Almost all control structures in C can be used the same way in C#

Similarities Expression statements, such as a = a + 5; Blocks, such as {a = 5; b = a;} if, if-else, switch, for, while, do-while, return, break, continue, and goto in C# are all similar to C

Differences The C# foreach loop provides for easy traversal of all elements in a collection try-catch-finally and throw in C# are related to exception handling Some more specialized statements have been added: checked, unchecked, using, lock and yield.

Program: Demonstrations of definite assignment.

using System; class DefiniteAssignmentDemo{ public static void Main(){ int a, b; bool c; if (ReadFromConsole("Some Number") < 10){ a = 1; b = 2; } else { a = 2; } Console.WriteLine(a); Console.WriteLine(b); // Use of unassigned local variable 'b' while (a < b){ c = (a > b); a = Math.Max(a, b); } Console.WriteLine(c); // Use of unassigned local variable 'c' } public static int ReadFromConsole(string prompt){ Console.WriteLine(prompt); return int.Parse(Console.ReadLine()); } }

Program: Demonstrations of if.

/* Right, Wrong */ using System; class IfDemo { public static void Main(){ int i = 0; /* if (i){ Console.WriteLine("i is regarded as true"); } else { Console.WriteLine("i is regarded as false"); } */ if (i != 0){ Console.WriteLine("i is not 0"); } else { Console.WriteLine("i is 0"); } } }

Program: Demonstrations of switch.

/* Right, Wrong */ using System; class SwitchDemo { public static void Main(){ int j = 1, k = 1; /* switch (j) { case 0: Console.WriteLine("j is 0"); case 1: Console.WriteLine("j is 1"); case 2: Console.WriteLine("j is 2"); default: Console.WriteLine("j is not 0, 1 or 2"); } */ switch (k) { case 0: Console.WriteLine("m is 0"); break; case 1: Console.WriteLine("m is 1"); break; case 2: Console.WriteLine("m is 2"); break; default: Console.WriteLine("m is not 0, 1 or 2"); break; } switch (k) { case 0: case 1: Console.WriteLine("n is 0 or 1"); break; case 2: case 3: Console.WriteLine("n is 2 or 3"); break; case 4: case 5: Console.WriteLine("n is 4 or 5"); break; default: Console.WriteLine("n is not 1, 2, 3, 4, or 5"); break; } string str = "two"; switch (str) { case "zero": Console.WriteLine("str is 0"); break; case "one": Console.WriteLine("str is 1"); break; case "two": Console.WriteLine("str is 2"); break; default: Console.WriteLine("str is not 0, 1 or 2"); break; } } }

Program: Demonstrations of foreach.

/* Right, Wrong */ using System; class ForeachDemo { public static void Main(){ int[] ia = {1, 2, 3, 4, 5}; int sum = 0; foreach(int i in ia) sum += i; Console.WriteLine(sum); } }

Program: Demonstrations of try catch.

/* Right, Wrong */ using System; class TryCatchDemo { public static void Main(){ int i = 5, r = 0, j = 0; /* r = i / 0; Console.WriteLine("r is {0}", r); */ try { r = i / j; Console.WriteLine("r is {0}", r); } catch(DivideByZeroException e){ Console.WriteLine("r could not be computed"); } } }

Functions Slide Annotated slide Contents Index References Textbook

On this page we will look at parameter passing techniques. C only supports call by value. Call by reference in C is in reality call by value passing of pointers. C# offers a variety of different parameter passing modes. We also discuss overloaded functions - functions of the same name distinguished by parameters of different types.

All functions in C# are members of classes or structs C# supports are variety of different function members: methods, properties, events, indexers, operators, and constructors

Similarities The basic ideas of function definition and function call are the same in C and C#

Differences Several different parameter passing techniques in C# Call by value. For input. No modifier. Call by reference. For input and output or output only Input and output: Modifier ref Output: Modifier out Modifiers used both with formal and actual parameters Functions with a variable number of input parameters in C# (cleaner than in C) Overloaded function members in C# First class functions (delegates) in C#

Program: Demonstration of simple functions in C#.

/* Right, Wrong */ using System; /* public int Increment(int i){ return i + 1; } public void Main (){ int i = 5, j = Increment(i); Console.WriteLine("i and j: {0}, {1}", i, j); } // end Main */ public class FunctionDemo { public static void Main (){ SimpleFunction(); } public static void SimpleFunction(){ int i = 5, j = Increment(i); Console.WriteLine("i and j: {0}, {1}", i, j); } public static int Increment(int i){ return i + 1; } }

Program: Demonstration of parameter passing in C#.

using System; public class FunctionDemo { public static void Main (){ ParameterPassing(); } public static void ValueFunction(double d){ d++;} public static void RefFunction(ref double d){ d++;} public static void OutFunction(out double d){ d = 8.0;} public static void ParamsFunction(out double res, params double[] input){ res = 0; foreach(double d in input) res += d; } public static void ParameterPassing(){ double myVar1 = 5.0; ValueFunction(myVar1); Console.WriteLine("myVar1: {0:f}", myVar1); // 5.00 double myVar2 = 6.0; RefFunction(ref myVar2); Console.WriteLine("myVar2: {0:f}", myVar2); // 7.00 double myVar3; OutFunction(out myVar3); Console.WriteLine("myVar3: {0:f}", myVar3); // 8.00 double myVar4; ParamsFunction(out myVar4, 1.1, 2.2, 3.3, 4.4, 5.5); // 16.50 Console.WriteLine("Sum in myVar4: {0:f}", myVar4); } }

Program: Demonstration of overloaded methods in C#.

using System; public class FunctionDemo { public static void Main (){ Overloading(); } public static void F(int p){ Console.WriteLine("This is F(int) on {0}", p); } public static void F(double p){ Console.WriteLine("This is F(double) on {0}", p); } public static void F(double p, bool q){ Console.WriteLine("This is F(double,bool) on {0}, {1}", p, q); } public static void F(ref int p){ Console.WriteLine("This is F(ref int) on {0}", p); } public static void Overloading(){ int i = 7; F(i); // This is F(int) on 7 F(5.0); // This is F(double) on 5 F(5.0, false); // This is F(double,bool) on 5, False F(ref i); // This is F(ref int) on 7 } }

Input and output Slide Annotated slide Contents Index References Textbook

Input and output (IO) is handled by a number of different classes in C#. In both C and C# there very few traces of IO in the languages as such.

Output to the screen and input from the keyboard is handled by the C# Console class File IO is handled by various Stream classes in C#

Similarities Console.Write and Console.WriteLine in C# correspond to printf in C

Differences There is no direct counterpart to C's scanf in C# Comprehensive formatting support of DateTime objects in C#

Program: Demonstrations of Console output in C#.

/* Right, Wrong */ using System; public class OutputDemo { // Placeholder syntax: {<argument#>[,<width>][:<format>[<precision>]]} public static void Main(){ Console.Write( "Argument number only: {0} {1}\n", 1, 1.1); // Console.WriteLine("Formatting code d: {0:d},{1:d}", 2, 2.2); Console.WriteLine("Formatting codes d and f: {0:d} {1:f}", 3, 3.3); Console.WriteLine("Field width: {0,10:d} {1,10:f}", 4, 4.4); Console.WriteLine("Left aligned: {0,-10:d} {1,-10:f}", 5, 5.5); Console.WriteLine("Precision: {0,10:d5} {1,10:f5}", 6, 6.6); Console.WriteLine("Exponential: {0,10:e5} {1,10:e5}", 7, 7.7); Console.WriteLine("Currency: {0,10:c2} {1,10:c2}", 8, 8.887); Console.WriteLine("General: {0:g} {1:g}", 9, 9.9); Console.WriteLine("Hexadecimal: {0:x5}", 12); Console.WriteLine("DateTime formatting with F: {0:F}", DateTime.Now); Console.WriteLine("DateTime formatting with G: {0:G}", DateTime.Now); Console.WriteLine("DateTime formatting with T: {0:T}", DateTime.Now); } }

Program: Output from the output demo program.

Argument number only: 1 1,1 Formatting codes d and f: 3 3,30 Field width: 4 4,40 Left aligned: 5 5,50 Precision: 00006 6,60000 Exponential: 7,00000e+000 7,70000e+000 Currency: kr 8,00 kr 8,89 General: 9 9,9 Hexadecimal: 0000c DateTime formatting with F: 4. juli 2008 15:35:31 DateTime formatting with G: 04-07-2008 15:35:31 DateTime formatting with T: 15:35:31

Program: Demonstrations of Console input in C#.

/* Right, Wrong */ using System; public class InputDemo { public static void Main(){ Console.Write("Input a single character: "); char ch = (char)Console.Read(); Console.WriteLine("Character read: {0}", ch); Console.ReadLine(); Console.Write("Input an integer: "); int i = int.Parse(Console.ReadLine()); Console.WriteLine("Integer read: {0}", i); Console.Write("Input a double: "); double d = double.Parse(Console.ReadLine()); Console.WriteLine("Double read: {0:f}", d); } }

Program: A sample dialog with the Console IO demo program. Input is shown in bold style. Boldface items represent the input entered by the user of the program.

Input a single character: a Character read: a Input an integer: 123 Integer read: 123 Input a double: 456,789 Double read: 456,79

References System.String.Format System.Console System.Int32 System.Double

Comments Slide Annotated slide Contents Index References Textbook

C# supports two different kinds of comments and XML variants of these

Single-line comments like in C++ // This is a single-line comment Delimited comments like in C /* This is a delimited comment */ XML single-line comments: /// <summary> This is a single-line XML comment </summary> XML delimited comments: /** <summary> This is a delimited XML comment </summary> */

XML comments can only be given before declarations, not inside other fragments Delimited comments cannot be nested

With respect to the basic language constructs, C# and Java are very close to each other

Types Richer repertoire in C# than in Java Operations Richer repertoire in C# than in Java

Strong overall similarities - Different with respect to a lot of details

Types Slide Annotated slide Contents Index References Textbook

Similarities. Classes in both C# and Java Interfaces in both C# and Java Differences. Structs in C#, not in Java Delegates in C#, not in Java Nullable types in C#, not in Java Class-like Enumeration types in Java; Simpler approach in C#

Operations Slide Annotated slide Contents Index References Textbook

Similarities: Operations in both Java and C# Methods Differences: Operations only in C# Properties Indexers Overloaded operators Anonymous methods

Other substantial differences Slide Annotated slide Contents Index References Textbook

Program organization No requirements to source file organization in C# Exceptions No catch or specify requirement in C# Nested and local classes Classes inside classes are static in C#: No inner classes like in Java Arrays Rectangular arrays in C# Virtual methods Virtual as well as non-virtual methods in C#

Program: Typical overall program structure of a Visual Basic Program.

Module MyModule Sub Main() Dim name As String ' A variable name of type string name = InputBox("Type your name") MsgBox("Hi, your name is " & name) End Sub End Module

Program: Typical overall program structure of a C# Program.

using System; class SomeClass{ public static void Main(){ string name; // A variable name of type string Console.WriteLine("Type your name"); name = Console.ReadLine(); Console.WriteLine("Hi, your name is " + name); } }

The Overall Picture Slide Annotated slide Contents Index References Textbook

Program organization Similar: Modul/Class in explicit or implicit namespace Program start Similar: Main Separation of program parts VB: Via line organization C#: Via use of semicolons Comments VB: From an apostrophe to the end of the line C#: From // to the end of the line or /* ... */ Case sensitiveness VB: Case insensitive. You are free to make your own "case choices". C#: Case sensitive. You must use the correct case for both keywords and you must be "case consistent" with respect to names.

Declarations and Types Slide Annotated slide Contents Index References Textbook

Program: A Visual Basic Program with a number of variable declarations.

Option Strict On Option Explicit On Module DeclarationsDemo Sub Main() Dim ch As Char = "A"C ' A character variable Dim b As Boolean = True ' A boolean variable Dim i As Integer = 5 ' An integer variable (4 bytes) Dim s As Single = 5.5F ' A floating point number (4 bytes) Dim d As Double = 5.5 ' A floating point number (8 bytes) End Sub End Module

Program: The similar C# program with a number of variable declarations.

using System; class DeclarationsDemo{ public static void Main(){ char ch = 'A'; // A character variable bool b = true; // A boolean variable int i = 5; // An integer variable (4 byges) float s = 5.5F; // A floating point number (4 bytes) double d = 5.5 ; // A floating point number (8 bytes) } }

Declaration and Types Slide Annotated slide Contents Index References Textbook

Declaration structure VB: Variable before type C#: Variable after type Types provide by the languages The same underlying types Known under slightly different names in VB and C#

VB and C# share the .NET types

Expressions and Operators Slide Annotated slide Contents Index References Textbook

Program: A Visual Basic Program with expressions and operators.

Option Strict On Option Explicit On Module ExpressionsDemo Sub Main() Dim i as Integer = 13 \ 6 ' i becomes 2 Dim r as Integer = 13 Mod 6 ' r becomes 1 Dim d as Double = 13 / 6 ' d becomes 2,16666666666667 Dim p as Double = 2 ^ 10 ' p becomes 1024 ' Dim b as Boolean i = 3 ' Illegal - Compiler error Dim b as Boolean, c as Boolean ' b and c are false (default values) c = b = true ' TRICKY: c becomes false End Sub End Module

Program: The similar C# program with a number of expressions and operators.

using System; class ExpressionsDemo{ public static void Main(){ int i = 13 / 6; // i becomes 2 int r = 13 % 6; // r becomes 1 double d = 13.0 / 6; // d becomes 2.16666666666667 double p = Math.Pow(2,10); // p becomes 1024 bool b = i == 3; // b becomes false bool c = b = true; // both b and c become true } }

Program: A Visual Basic Program with expressions and operators.

Option Strict On Option Explicit On Module ExpressionsDemo Sub Main() Dim i as Integer = 2, r as Integer = 1 If i <> 3 Then Console.WriteLine("OK") ' Writes OK End If If Not i = 3 Then Console.WriteLine("OK") ' Same as above End If End Sub End Module

Program: The similar C# program with a number of expressions and operators.

using System; class ExpressionsDemo{ public static void Main(){ int i = 2, r = 1; if (i != 3) Console.WriteLine("OK"); // Writes OK if (!(i == 3)) Console.WriteLine("OK"); // Same as above } }

Program: A Visual Basic Program with expressions and operators.

Option Strict On Option Explicit On Module ExpressionsDemo Sub Main() Dim i as Integer = 2, r as Integer = 1 If i = 3 AndAlso r = 1 Then ' Writes OK Console.WriteLine("Wrong") Else Console.WriteLine("OK") End If If i = 3 OrElse r = 1 Then ' Writes OK Console.WriteLine("OK") Else Console.WriteLine("Wrong") End If End Sub End Module

Program: The similar C# program with a number of expressions and operators.

using System; class ExpressionsDemo{ public static void Main(){ int i = 2, r = 1; if (i == 3 && r == 1) Console.WriteLine("Wrong"); else Console.WriteLine("OK"); if (i == 3 || r == 1) Console.WriteLine("OK"); else Console.WriteLine("Wrong"); } }

Expressions and Operators Slide Annotated slide Contents Index References Textbook

Operator Precedence Major differences between the two languages

References Operator precedence in C# VB operator precedence

Equality and Assignment VB: Suffers from the choice of using the same operator symbol = for both equality and assignment VB: The context determines the meaning of the operator symbol = C#: Separate equality operator == and assignment operator = Remarkable operators VB: Mod, &, \, And, AndAlso, Or, OrElse C#: ==, !, %, ?:

Control Structures for Selection Slide Annotated slide Contents Index References Textbook

Program: A Visual Basic Program with an If Then Else control structure.

Module IfDemo Sub Main() Dim i as Integer, res as Integer i = Cint(InputBox("Type a number")) If i < 0 Then res = -1 Console.WriteLine("i is negative") Elseif i = 0 res = 0 Console.WriteLine("i is zero") Else res = 1 Console.WriteLine("i is positive") End If Console.WriteLine(res) End Sub End Module

Program: The similar C# program with an if else control structure.

using System; class IfDemo{ public static void Main(){ int i, res; i = Int32.Parse(Console.ReadLine()); if (i < 0){ res = -1; Console.WriteLine("i is negative"); } else if (i == 0) { res = 0; Console.WriteLine("i is zero"); } else { res = 1; Console.WriteLine("i is positive"); } Console.WriteLine(res); } }

Program: A Visual Basic Program with a Select control structure.

Module IfDemo Sub Main() Dim month as Integer = 2 Dim numberOfDays as Integer Select Case month Case 1, 3, 5, 7, 8, 10, 12 numberOfDays = 31 Case 4, 6, 9, 11 numberOfDays = 30 Case 2 numberOfDays = 28 ' or 29 Case Else Throw New Exception("Problems") End Select Console.WriteLine(numberOfDays) ' prints 28 End Sub End Module

Program: The similar C# program with a switch control structure.

using System; class CaseDemo{ public static void Main(){ int month = 2, numberOfDays; switch(month){ case 1: case 3: case 5: case 7: case 8: case 10: case 12: numberOfDays = 31; break; case 4: case 6: case 9: case 11: numberOfDays = 30; break; case 2: numberOfDays = 28; break; // or 29 default: throw new Exception("Problems"); } Console.WriteLine(numberOfDays); // prints 28 } }

Control structures for Selection Slide Annotated slide Contents Index References Textbook

If-then-else Similar in the two languages Case C#: Efficient selection of a single case - via underlying jumping VB: Sequential test of cases - the first matching case is executed VB: Select Case approaches the expressive power of an if-then-elseif-else chain Case "fall through" is disallowed in both languages

Control Structures for Iteration Slide Annotated slide Contents Index References Textbook

Program: A Visual Basic Program with a while loop.

Module WhileDemo Sub Main() Dim large As Integer = 106, small As Integer = 30 Dim remainder As Integer While small > 0 remainder = large Mod small large = small small = remainder End While Console.WriteLine("GCD is {0}", large) ' Prints 2 End Sub End Module

Program: The similar C# program with a while loop.

using System; class WhileDemo{ public static void Main(){ int large = 106, small = 30, remainder; while (small > 0){ remainder = large % small; large = small; small = remainder; } Console.WriteLine("GCD is {0}", large); // Prints 2 } }

Program: A Visual Basic Program with a for loop.

Module ForDemo Sub Main() Dim sum As Integer = 0 For i as Integer = 1 To 10 sum = sum + i Next i Console.WriteLine("The sum is {0}", sum) ' Prints 55 End Sub End Module

Program: The similar C# program with a for loop.

using System; class ForDemo{ public static void Main(){ int sum = 0; for(int i = 1; i <= 10; i++) sum = sum + i; Console.WriteLine("The sum is {0}", sum); // Prints 55 } }

Program: A Visual Basic Program with a Do Loop.

Option Strict On Option Explicit On Module DoDemo Sub Main() Const PI As Double = 3.14159 Dim radius As Double, area As Double Do radius = Cdbl(InputBox("Type radius")) If radius < 0 Then Exit Do End If area = PI * radius * radius Console.WriteLine(area) Loop End Sub End Module

Program: The similar C# program with a similar for and a break.

using System; class ForDemo{ public static void Main(){ const double PI = 3.14159; double radius, area; for(;;){ radius = double.Parse(Console.ReadLine()); if (radius < 0) break; area = PI * radius * radius; Console.WriteLine(area); } } }

Control structures for iteration Slide Annotated slide Contents Index References Textbook

While Very similar in C# and VB C#: Does also support a do ... while Do Loop VB: Elegant, powerful, and symmetric. No direct counterpart in C# For C#: The for loop is very powerful. VB: Similar to classical for loop from Algol and Pascal

Arrays Slide Annotated slide Contents Index References Textbook

Program: A Visual Basic Program with an array of 10 elements.

Option Strict On Option Explicit On Module ArrayDemo Sub Main() Dim table(9) as Integer ' indexing from 0 to 9. For i as Integer = 0 To 9 table(i) = i * i Next For i as Integer = 0 To 9 Console.WriteLine(table(i)) Next End Sub End Module

Program: The similar C# program with an array of 10 elements.

using System; class ArrayDemo{ public static void Main(){ int[] table = new int[10]; // indexing from 0 to 9 for(int i = 0; i <= 9; i++) table[i] = i * i; for(int i = 0; i <= 9; i++) Console.WriteLine(table[i]); } }

Arrays Slide Annotated slide Contents Index References Textbook

Notation VB: a(i) C#: a[i] Range Both from zero to an upper limit VB: The highest index is given in an array variable declaration C#: The length of the array is given in an array variable declaration

Procedures and Functions Slide Annotated slide Contents Index References Textbook

Program: A Visual Basic Program with a procedure - Subprogram.

Option Strict On Option Explicit On Module ArrayDemo Sub Sum(ByVal table() As Integer, ByRef result as Integer) result = 0 For i as Integer = 0 To 9 result += table(i) Next End Sub Sub Main() Dim someNumbers(9) as Integer Dim theSum as Integer = 0 For i as Integer = 0 To 9 someNumbers(i) = i * i Next Sum(someNumbers, theSum) Console.WriteLine(theSum) End Sub End Module

Program: The similar C# program with void method.

using System; class ProcedureDemo{ public static void Sum(int[] table, ref int result){ result = 0; for(int i = 0; i <= 9; i++) result += table[i]; } public static void Main(){ int[] someNumbers = new int[10]; int theSum = 0; for(int i = 0; i <= 9;i++) someNumbers[i] = i * i; Sum(someNumbers, ref theSum); Console.WriteLine(theSum); } }

Program: A Visual Basic Program with a function.

Option Strict On Option Explicit On Module ArrayDemo Function Sum(ByVal table() As Integer) as Integer Dim result as Integer = 0 For i as Integer = 0 To 9 result += table(i) Next return result End Function Sub Main() Dim someNumbers(9) as Integer Dim theSum as Integer = 0 For i as Integer = 0 To 9 someNumbers(i) = i * i Next theSum = Sum(someNumbers) Console.WriteLine(theSum) End Sub End Module

Program: The similar C# program with int method.

using System; class ProcedureDemo{ public static int Sum(int[] table){ int result = 0; for(int i = 0; i <= 9; i++) result += table[i]; return result; } public static void Main(){ int[] someNumbers = new int[10]; int theSum = 0; for(int i = 0; i <= 9;i++) someNumbers[i] = i * i; theSum= Sum(someNumbers); Console.WriteLine(theSum); } }

Procedures and Functions Slide Annotated slide Contents Index References Textbook

Procedures VB: Subprogram C#: void method (void function) Functions VB: Functions C#: int method or someType method Parameter passing Both languages support call by value and call by reference

Combined C# and Visual Basic Programming Slide Annotated slide Contents Index References

A client written in Visual Basic and a server written in C#

Program: A class Die programmed in C#.

using System; public class Die { private int numberOfEyes; private Random randomNumberSupplier; private const int maxNumberOfEyes = 6; public Die(){ randomNumberSupplier = new Random(unchecked((int)DateTime.Now.Ticks)); numberOfEyes = NewTossHowManyEyes(); } public void Toss(){ numberOfEyes = NewTossHowManyEyes(); } private int NewTossHowManyEyes (){ return randomNumberSupplier.Next(1,maxNumberOfEyes + 1); } public int NumberOfEyes() { return numberOfEyes; } public override String ToString(){ return String.Format("[{0}]", numberOfEyes); } }

Program: A client of class Die programmed in Visual Basic.

Imports System Module DieApplication Sub Main() Dim D1 as new Die() Dim D2 as new Die() D1.Toss() Console.WriteLine(D1) Console.WriteLine() For i as Integer = 1 To 10 D2.Toss() Console.WriteLine(D2) Next i End Sub End Module

Program: Compilation and execution.

csc /t:library die.cs vbc /r:die.dll client.vb client

Object-oriented programming in Visual Basic Slide Annotated slide Contents Index References Textbook

Both VB and C# supports object-oriented programming on the .Net platform

Microsoft supplies several different set of tools that support the C# programmer

.NET Framework SDK 3.5 "Software Development Kit" Command line tools, such as the C# compiler csc Visual C# Express IDE - An Integrated Development Environment A C# specialized, free version of Microsoft Visual Studio 2008 Visual Studio IDE - An Integrated Development Environment The professional, commercial development environment for C# and other programming languages

Reference C# Express Video Lectures

Only on Windows...

C# Tools on Unix Slide Annotated slide Contents Index References Textbook

The MONO project provides tools for C# development on Linux, Solaris, Mac OS X, Windows, and Unix.

MONO An open source project (sponsored by Novell) Corresponds the the Microsoft SDK Based on ECMA specifications of C# and the Common Language Infrastructure (CLI) Virtual Machine Command line tools Compilers: mcs (C# 1.5) and gmcs (C# 2.0) MONO on cs.aau.dk Mono is already installed on the application servers at cs.aau.dk MONO on your own Linux machine You can install MONO yourself if you wish MonoDevelop A GNOME IDE for C#

MONO is not as updated as the Microsoft C# solutions

Documentation Tools Slide Annotated slide Contents Index References Textbook

It is important to have access to documentation of the C# standard class library

Local documentation The SDK 3.5 comes with a special documentation browser Visual C# Express has integrated documentation available Documentation from a Microsoft webserver Link from the course home page - C# resources

Collected references Contents Index

Computer Language History The struct System.Decimal The struct System.Double The struct System.Single The struct System.UInt64 The struct System.Int64 The struct System.UInt32 The struct System.Int32 The struct System.UInt16 The struct System.Int16 The struct System.Byte The struct System.Sbyte Decimal Floating Point in .NET The struct System.Char System.Enum System.String System.Array Similar table for C System.Double System.Int32 System.Console System.String.Format VB operator precedence Operator precedence in C# C# Express Video Lectures

Chapter 2: Introduction to C#
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