Hello, World!

    #include <stdio.h>
    #include <math.h>

    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;
    }