change a pointer of address of another application

change a pointer of address of another application

I need somebody to edit the title, I can't find better title.



Assume a have this simple program called source.exe:
#include <stdio.h>
int main()
{
int a = 5;
printf("%p", &a);
return 0;
}
I want to write another application, change.exe, that changes a in the above.
I tried something like this:
int main()
{
int * p = (int*) xxx; // xxx is what have printed above
*p = 1;
printf("%d", *p);
return 0;
}
It doesn't work. assuming I have Administrator rights, is there a way to
do what I've tried above? thanks.