qsort() is a Utility Function that is used to quick sort an array. The "size", number of elements ("num") is specified in this function.

    void qsort(void *buf, size_t num, size_t size,
           int (*compare) (const void *, const void *));  

In the above syntax "compare" is used to compare the elements with a keys of an array. This function returns "0" if both arguments are equal, if "arg1" is less than "arg2" the a negative value is returned. If "arg1" is greater then a positive value is returned by the function. The following is the syntax of this function.

   int func_name(const void *arg1, const void *arg2);

   #include <stdlib.h>
   #include <stdio.h>
   #include <string.h>
   int main ()
     {
        int i;
        char arr[3][20] = {"2", "1", "3" };
        qsort(arr,3, 20, (int(*) (const void*, 
               const void*))strcmp);
        printf("The sorted array\n");
        for (i=0; i<3; ++i)
           printf ("%s\n", arr[i]);
        return 0;
     }

   The sorted array
    1
    2
    3

In the above example qsort() function is used to sort the array in descending order.