Mid Point Circle Drawing Algorithm

#include <GL/gl.h>
#include <GL/glut.h>
void display(void)
{
    glClear (GL_COLOR_BUFFER_BIT);

    glColor3f (1.0, 1.0, 1.0);

    int x=0, y=40;
    int p=1-y;

    int ax[1111];
    int ay[1111];
    int idx=0;
    ax[idx]=x;
    ay[idx++]=y;
    while(1){
        if(p<0){
            x++;
            p=p+(2*x)+1;
        }
        else{
            x++;
            y--;
            p=p+(2*x)+1-2*y;
        }
        ax[idx]=x;
        ay[idx++]=y;
        if(x>=y) break;
    }

    glBegin(GL_POINTS);
    int tx,ty;
    for(int i=0;i<idx;i++){
        tx=ax[i]*(-1);
        ty=ay[i]*(-1);

        glVertex2d(ax[i],ay[i]);
        glVertex2d(tx,ay[i]);
        glVertex2d(ax[i],ty);
        glVertex2d(tx,ty);

        glVertex2d(ay[i],ax[i]);
        glVertex2d(ty,ax[i]);
        glVertex2d(ay[i],tx);
        glVertex2d(ty,tx);
    }

    glColor3f (1.0, 0.0, 0.0);

    for(int i=-60;i<=60;i++){
        glVertex2d(0,i);
        glVertex2d(i,0);
    }


    glEnd();

    glFlush ();
}

void init (void){

    glClearColor (0.0, 0.0, 0.0, 0.0);

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluOrtho2D(-100,100,-100,100);      //fix the windows size
}

int main(int argc, char** argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
    glutInitWindowSize (1000, 1000);
    glutInitWindowPosition (50, 50);
    glutCreateWindow ("172-15-9804");
    init ();
    glutDisplayFunc(display);
    glutMainLoop();

    return 0;
}