#include <stdio.h>

void func( int *p )
{
   // The expression  *p   will access the ORIGINAL  variable !!

   *p = *p + 1;   // Add 1 to the (original) variable
}

int main(int argc, char *argv[])
{
    int x1 = 4, x2 = 88;

    printf("x1 before = %d\n", x1);
    func( &x1 );		// Pass address of x1 to function  
    printf("x1 after  = %d\n", x1);

    printf("x2 before = %d\n", x2);
    func( &x2 );		// Pass address of x2 to function
    printf("x2 after  = %d\n", x2);
}