When I use an INT program, something goes wrong.

Here's a little example:

int main()
{
cout<<"Stupid int main thingy!! I'm sick of it!!";
system("PAUSE");
return 0;
}

It runs fine the first time, but when I try again it says "implicit declaration of function `int system(...)'"

In order to get it going again, I have to start a new project.

Anybody know what's going on and how to fix it?

Thanks.