Sleep for N seconds and wait for keypress

I want to write a program in C that performs some function and then sleeps for some minutes. During this sleep period I would like to do something and exit if a key is pressed.

int main()
{
    while(1)
    {
        /*body*/
        sleep(300);
    }
    /*some lines here*/
    return 0;
}

Is there anyway that I can exit the loop during either the sleep period or at any time using a non-blocking key listener?

Just don't sleep for 300 seconds but rather 300 x for 1 second and check for key press:

int main()
{
    while(1)
    {
        /*body*/
        for ( int i=0; i<300; i++ )
        {
            if (keypressed())
                doSomething();
        }
    }
    /*some lines here*/
    return 0;
}

EDIT: Why the while (1) in your code? Do you really want to run your program endlessly? (In that case, /*some lines here*/ doesn't make sense.)