how to move a object inside a certain boundry in c++

Question

i want to make a ping pong game, i am stuck at the ball movement i don't want it to get out of the boundaries which in case is 640 by 480..... i don't want it to get out of this boundary but instead move again just like in the case of collision... following is the code

#include <iostream>
#include <graphics.h>
#include <stdio.h>
#include <conio.h>

int main()
{
    int gd = DETECT, gm;
    initgraph(&gd, &gm, "C:\\TC\\BGI");
    int x = 0, y = 0, i;
    setcolor(RED);
    setfillstyle(SOLID_FILL, YELLOW);
    circle(x, y, 20);
    floodfill(x, y, RED);
loop1:
    for (i = 0; i <= 45; i++) {
        cleardevice();
        setcolor(RED);
        setfillstyle(SOLID_FILL, YELLOW);
        circle(x, y, 20);
        floodfill(x, y, RED);
        if (y == 460) {
            break;
        }
        else {
            x += 10;
            y += 10;
        }
        delay(10);
    }

    for (i = 0; i <= 46; i++) {
        cleardevice();
        setcolor(RED);
        setfillstyle(SOLID_FILL, YELLOW);
        circle(x, y, 20);
        floodfill(x, y, RED);
        if (x == 620) {
            break;
        }
        else {
            x += 10;
            y -= 10;
        }
        delay(10);
    }

    for (i = 0; i <= 45; i++) {
        cleardevice();
        setcolor(RED);
        setfillstyle(SOLID_FILL, YELLOW);
        circle(x, y, 20);
        floodfill(x, y, RED);
        if (y == 20) {
            break;
        }
        else {
            x -= 10;
            y -= 10;
        }
        delay(10);
    }

    for (i = 0; i <= 45; i++) {
        cleardevice();
        setcolor(RED);
        setfillstyle(SOLID_FILL, YELLOW);
        circle(x, y, 20);
        floodfill(x, y, RED);
        if (x == 20) {
            goto loop1;
        }
        else {
            x -= 10;
            y += 10;
        }
        delay(10);
    }
    getch();
    closegraph();
}

The lake of indentation, the use of `goto` and the inclusion of all your graphics code makes this example rather hard understand. The simpler your example, the more likely you are that someone will take the time to understand it. You should properly indent and reduce your example to it's essential components. Additionally, the use of local files (`"C:\\TC\\BGI"`) makes this example unrunnable for others, further discouraging help. — François Andrieux, Feb 09 '17 at 20:49
That is the worst usage of `goto` that you could have. Branching upwards to a label, out of a `for` loop back into a `for` loop using an integer `i` as a loop counter.in both loops you're jumping out of and into again. [Spaghetti code](https://en.wikipedia.org/wiki/Spaghetti_code) — PaulMcKenzie, Feb 09 '17 at 20:55

Alex · Accepted Answer · 2017-02-09T20:54:16.747

A simple way for the collision effect at the boundries, is that you negate the y-Component of the Pong movement, when it "hits" the upper or lower boundry and negate the x-Component when it "hits" the left or right boundry.

Short example code:

int speedvector[2];
speedvector[0] = 10;
speedvector[1] = 10;

int pongposition[2];
pongposition[0] = 100;
pongposition[1] = 100;

Main game loop:

while(gameon){
  if(pongposition[0] < 0 || pongposition[0] > 640){
    speedvector[0] = -speedvector[0];
  }
  if(pongposition[1] < 0 || pongposition[1] > 480){
    speedvector[1] = -speedvector[1];
  }
  pongposition[0] += speedvector[0];
  pongposition[1] += speedvector[1];
}

how to move a object inside a certain boundry in c++

1 Answers1