$ cat foo.c
#include <stdio.h>
#include <stdlib.h>

int compare_int(const void *a, const void *b) {
    return *(int *)a - *(int *)b;
}

int compare_double(const void *a, const void* b) {
    return *(double *)a - *(double *)b;
}

int     a1[] = { 1, 100, 5, 50, 25 };
double  a2[] = { 1.0, 10.0, 5.0, 25.0 };

int (*cmp_fn)(const void *, const void *);

#define CFG_ADD(TYPE) cmp_fn = compare_ ## TYPE;

int main(int argc, char **argv) {
    CFG_ADD(int);
    qsort(a1, sizeof(a1)/sizeof(a1[0]), sizeof(a1[0]), cmp_fn);
    for (int i=0; i<sizeof(a1)/sizeof(a1[0]); i++) {
        printf("%d, ", a1[i]);
    }

    printf("\n\n");

    CFG_ADD(double);
    qsort(a2, sizeof(a2)/sizeof(a2[0]), sizeof(a2[0]), cmp_fn);
    for (int i=0; i<sizeof(a2)/sizeof(a2[0]); i++) {
        printf("%f, ", a2[i]);
    }
}

$ gcc foo.c -o foo
$ ./foo
1, 5, 25, 50, 100,

1.000000, 5.000000, 10.000000, 25.000000,