How to stop the constant flickering while playing animation?

Question

I was trying to make a simple animation of a stickman walking, in graphics library in C.

My code:

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

void swap(int *x, int *y){

    int temp=0;
    temp=*x;
    *x=*y;
    *y=temp;
}


int main(){
    int gd=DETECT,gm=0;
    int i=0;
    int a=30+i;
    int b=50+i;
    initgraph(&gd,&gm,"C:\\TURBOC3\\BGI");
    while(i!=600){
    swap(&a,&b);
    circle(40+i,40,30);
    line(40+i,70,a+i,90);
    line(40+i,70,b+i,90);
    i++;
    delay(10);
    cleardevice();
    }
    getch();
    closegraph();
    return 0;
}

The problem is that, the monitor screen keeps flickering constantly while playing the animation and moreover, the leg positions are not swapping according to the swap(&b,&c) function. Where am I going wrong here? Can someone please help me?

Fix: So, I realised that, there's no point in having the swap() function as, swapping the lines will make the alignment same again for both of them (as a result it will look like the legs are not moving), so I decided to tweak some things here:

while(i!=600){
    if(i%2==0){
        circle(40+i,40,30);
        line(40+i,70,(a+b)/2+i,90);
        line(40+i,70,(b+a)/2+i,90);

    }else{
        circle(40+i,40,30);
        line(40+i,70,a+i,90);
        line(40+i,70,b+i,90);
    }
    i++;
    delay(10);
    cleardevice();
    }

Now, it actually looks like the figure is walking. But I still don't know how to fix the screen flickering problem.