为啥要两个%%

#include <stdio.h>

int main()

{

    int x,y;

    x = 10;

    y = -3;

    printf("x+y=%d\n",x+y);  

    printf("x-y=%d\n",x-y);

    printf("x*y=%d\n",x*y);

    printf("x/y=%d\n",x/y);

    printf("x%%y=%d\n",x%y);  

    return 0;    

}