小球碰撞弹回操作

#include <graphics.h>
#include <conio.h>
#include <time.h>

int main(){
    srand((unsigned)time(NULL));
    initgraph(640, 480);

    //int x = 21, y = 21;
    int x = rand() % 598 + 21;
    int y = rand() % 438 + 21;
    
    //int a = 1, b = 1;
    int a = rand() % 5 + 1;
    int b = rand() % 5 + 1;
    while (1){

        cleardevice();
        BeginBatchDraw();
        setcolor(GREEN);
        setfillcolor(GREEN);
        fillcircle(x, y, 20);
        // 边界判定
        if (x < 20 || x > 620){   
            a *= -1;
        }
        if (y < 20 || y > 460){
            b *= -1;
        }

        x += a;
        y += b;
        Sleep(10);
        EndBatchDraw();
    }

    closegraph();
    return 0;
}

// 在640 * 480 内随机一个位置产生一个小球 ，

碰到边框弹回