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Exercise solution 3.4
Indlæsning af heltal

Mit program, som løser problemet, er følgende:

/* Læs et tal fra en linie af tegn, og retur det pågældende tegn som en int */

import java.io.*; // for at kunne anvende BufferedReader mv.

class talLaesning {

  //et objekt, kaldet stdin, som tillader os at læse en tekst linie:
  static BufferedReader stdin = new BufferedReader (new InputStreamReader(System.in));

  public static int readInt() throws IOException{
  /* Read an integer from the keyboard, and return it as the result of this function */

     String textLine;
     char nextCifferChar;
     int nextCiffer;
     textLine = stdin.readLine();
     
     int i, tal;
     boolean positive = true;    // the sign of the number
     boolean cifferRead = false; // have we seen the first ciffer
     tal = 0;
     for(i=0; i<textLine.length(); i++){
       nextCifferChar = textLine.charAt(i);
       if (Character.isDigit(nextCifferChar)){
            cifferRead = true;
            nextCiffer = Character.digit(nextCifferChar,10);
            tal = tal * 10 + nextCiffer;
       }
       else if (nextCifferChar == '-' && !cifferRead) {
            positive = !positive;
       }
       else if (nextCifferChar == '+' && !cifferRead) {
	 // just ignore it
       } 
       else System.out.println(nextCifferChar + " er et ulovligt tegn");
     }
     return positive ? tal : -tal;    
  }
  

  public static void main (String[] ars) throws IOException{
     System.out.println("Indlaes et tal");
     int etTal = readInt();
     System.out.println("Tallet var: " +  etTal);
  }

}