Answers for "qsort"

qsort in c

#include <stdlib.h>
int cmpfunc (const void * a, const void * b) {
   return ( *(int*)a - *(int*)b );
}

int main () {
//n is number of elements in arr(size f that arr)
   qsort(arr, n, sizeof(int), cmpfunc);
   }

quick sort predefined function in c++

#include <cstdlib>

//declare compare
int compare(const void* a, const void* b)
{
	const int* x = (int*) a;
	const int* y = (int*) b;

	if (*x > *y)
		return 1;
	else if (*x < *y)
		return -1;

	return 0;
}

//fuction used
qsort(arr,num,sizeof(int),compare);

qsort

#include <stdlib.h>

/* Comparison function. Receives two generic (void) pointers to the items under comparison. */
int compare_ints(const void *p, const void *q) {
    int x = *(const int *)p;
    int y = *(const int *)q;

    /* Avoid return x - y, which can cause undefined behaviour
       because of signed integer overflow. */
    if (x < y)
        return -1;  // Return -1 if you want ascending, 1 if you want descending order. 
    else if (x > y)
        return 1;   // Return 1 if you want ascending, -1 if you want descending order. 

    return 0;
    // All the logic is often alternatively written:
    return (x > y) - (x < y);
}

/* Sort an array of n integers, pointed to by a. */
void sort_ints(int *a, size_t n) {
    qsort(a, n, sizeof(*a), compare_ints);
}