#include <stdio.h>

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

 return 0;
 }