Hello, World!

int main( )
{
    double a, d, x = 0.0, y = 0.0, temp = 0.0;
    int n, i;
    scanf( "%lf%lf%d", &a, &d, &n );

    for( i = 0; i < n; i ++ ) {
        // temp += d;
        // if( temp > 4.0 * a ) temp = fmod( temp, 4.0 * a );
        temp = fmod( temp + d, 4.0 * a );

        if( temp < a ) {
            x = temp;
            y = 0.0;
        }
        else if( temp < a + a ) {
            x = a;
            y = temp - a;
        }
        else if( temp < a + a + a ) {
            x = a - ( temp - a - a );
            y = a;
        }
        else {
            x = 0.0;
            y = a - ( temp - a - a - a );
        }
        printf( "%.10lf %.10lf\n", x, y );
    }

    return 0;
}