Thread: Callback function in C, but problem with rand() and srand() function

i've just write a code test, but rand() and srand() seem not to be work. Please show me what happens! . thanks a lot.

Code:

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
int cmp(void const* a, void const* b) { return ( *(int*)a - *(int*)b ); }
int main() {
    srand( (unsigned int) time(NULL) ); int ar[10],i;
    // fill array
    for (i = 0; i < 10; ++i)
        ar[i] = rand()%20+1; // range (1->20)
    // print before sort
    for (i = 0; i < 10; ++i)
        printf("%d ", i);
    // quick sort
    qsort( (void*)ar, 10, sizeof(int), cmp );
    // print after sort
    printf("\n");
    for (i = 0; i < 10; ++i)
        printf("%d ", i);
    return 0;
}

the output not to be changes once i run program, the output is fixed:
0 1 2 3 4 5 6 7 8 9
0 1 2 3 4 5 6 7 8 9

Beware what you are printing:

Code:

    // print before sort
    for (i = 0; i < 10; ++i)
        printf("%d ", i);
    for (i = 0; i < 10; ++i)
    // print after sort
        printf("%d ", i);