 | void order_chars(char *c1, char *c2, char *c3); void swap(char *p, char *q); |
We define prototypes of the two functions order_chars and swap, such that they are known by the main method. |
#include <stdio.h>
void order_chars(char *c1, char *c2, char *c3);
void swap(char *p, char *q);
int main(void) {
char c1 = 'c', c2 = 'b', c3 = 'd';
printf("%c, %c, %c\n", c1, c2, c3);
order_chars(&c1, &c2, &c3);
printf("%c, %c, %c\n", c1, c2, c3);
return 0;
}
void order_chars(char *c1, char *c2, char *c3){
if (*c3 < *c2) swap(c2,c3);
if (*c2 < *c1) swap(c1,c2);
if (*c3 < *c2) swap(c2,c3);
}
void swap(char *p, char *q){
int tmp;
tmp = *p;
*p = *q;
*q = tmp;
}
| void order_chars(char *c1, char *c2, char *c3); void swap(char *p, char *q); |
We define prototypes of the two functions order_chars and swap, such that they are known by the main method. |
| int main(void) {
char c1 = 'c', c2 = 'b', c3 = 'd';
printf("%c, %c, %c\n", c1, c2, c3);
order_chars(&c1, &c2, &c3);
printf("%c, %c, %c\n", c1, c2, c3);
return 0;
} |
We define three character variables c1, c2, and c3. We pass the addresses of these variables to order_chars. In that way, order_chars can change the values of the variables for us, which is exactly what we want. Recall that we go for a re-ordering of the values of c1, c2, and c3 such that their values appear as sorted. |
| void order_chars(char *c1, char *c2, char *c3){
if (*c3 < *c2) swap(c2,c3);
if (*c2 < *c1) swap(c1,c2);
if (*c3 < *c2) swap(c2,c3);
} |
The function order_chars receives three pointers to chars. In other words, it uses call by reference parameters. First it compares the values of *c3 and *c2. Hereby the two last characters passed to order_chars are compared. If they are out of order, we use the function swap to exchange their values. Next, *c2 and *c1 are compare and maybe swaped. These two steps ensure that *c1 is the smallest. The next step ensures that *c2 is smaller than *c3. If not, we swap these too. Then we are done. We can notice that our sorting strategy is quite similar to bubble sort applied on a three element array. |
| void swap(char *p, char *q){
int tmp;
tmp = *p;
*p = *q;
*q = tmp;
} |
The function is swap we have seen before, so we will not comment on it here. It is explained in the text book. |