C/C++ :: How To End A While Loop After Set Time

I am trying to make this while loop cut out / self break after 3 seconds. It is part of a simple game I am creating that gives the users 3 seconds to react otherwise it moves on to the next part.

while(1) {
key=getch();
if(key=='a'||key=='k'||key=='g') {
break;
}
}

All I need is it to end after 3 seconds, the rest of the code is working fine.

This sort of thing:

long startTime = System.currentTimeMillis(); //fetch starting time
while(false||(System.currentTimeMillis()-startTime)<10000)
If it IS for C, then I implemented it wrong or something.