#include <stdio.h>//修正後

struct s {
    int x;
    int y;
};

int main(void)
{
    struct s a = {10, 20};
    struct s b = {10, 20};
    struct s c = {30, 40};

    if (a.x == b.x) a.x = c.x;
    printf("a.x = %d\n", a.x);

    a = b;

    if (a.x == b.x && a.y == b.y) a = c;
    printf("a.y = %d\n", a.y);

    return 0;
}