Why the function pointer pointing to different function works than it is defined

Why the function pointer pointing to different function works than it is
defined

In the following program the function pointer is defined to point to a
function which accepts no argument and returns void yet the function
pointer works here. Why?
#include<stdio.h>
int mul(int*,int*);
void main()
{ int a=10,b=20;
int(*p)();
p=&mul;
printf("%d ", (*p)(&a,&b));
}
int mul(int*a,int*b)
{
return (*a * *b);
}