Ok, mersi!

Am si eu o intrebare: De ce anume imi da aceste erori ?
http://prntscr.com/uefct

Acesta e codul:

Cod:

#include<iostream.h>
#include<fstream.h>
int main()
{
	ifstream f("cmmdc.in");
	ofstream g("cmmdc.out");
	f>>a>>b;
	if(a>b)a=a-b;
	else b=b-a;
	g<<a;
	f.close();
	g.close();
}