สอบถามเรื่องการเขียนฟังชั่น pass by value หน่อยครับ

#include <stdio.h>
#include <conio.h>
struct Data{
	int x,y;
}s1,s2;
void Swap( ){
	
}

int main(){
	s1.x = 3; s1.y=3; s2.x=5; s2.y=5;
	printf("Before swap s1.x = %d, s1.y = %d \n",s1.x,s1.y);
	printf("After swap s2.x = %d, s2.y = %d \n",s2.x,s2.y);
	Swap(Data *s1,Data *s2);
	printf("Before swap s1.x = %d, s1.y = %d \n",s1.x,s1.y);
	printf("After swap s2.x = %d, s2.y = %d ",s2.x,s2.y);
	getch();	
}