sort_struct.c

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

struct Point {
    char index;
    int x, y;
};


int compare_struct(const void *a, const void *b){

    struct Point *aa = (struct Point*)a;
    struct Point *bb = (struct Point*)b;

    // compare x*y

    long long res_a = ((long long)aa->x * aa->y);
    long long res_b = ((long long)bb->x * bb->y);

    if(res_a > res_b)
        return 1;
    else if (res_a == res_b)
        return 0;
    else
        return -1;
}


int main(){

    struct Point arr[10];
    const int count = 10;

    srand(time(0));

    for(int i = 0 ; i < count; i++)
        arr[i] = (struct Point){.x = rand()%200, .y= rand()%200, .index=i};

    // before sort
    for(int i = 0; i < count ;i++){
        printf("Point #%d\n\tindex: %d, x: %d, y: %d\n", i, arr[i].index, arr[i].x, arr[i].y);
    }

    printf("----\n");

    qsort(arr, count, sizeof(struct Point), compare_struct);

    // after sort
    for(int i = 0; i < count ;i++){
        printf("Point #%d\n\tindex: %d, x: %d, y: %d\n", i, arr[i].index, arr[i].x, arr[i].y);
    }


    return 0;
}