#include <fstream.h>
ifstream f("in.txt");
ofstream g("out.txt");
int main ()
{
int n,i;
f>>n;
for (i=1;i<=n*n;i++)
g<<i<<" ";
return 0;
}

I know it isn't what it should do, but still how can it get time limit exceeded??? I don't get it :)

Don't read from the file and you will get your WA :)