opengl c++ easy colision source PUSH START and up

#include  "GL/glut.h"
#include  "stdlib.h"
GLfloat d = 0.1;

//core dumpted to rebulid

GLfloat wekt;
GLfloat wekt2;

int flag=1;
GLfloat x1=-0.0;
GLfloat y1 =0.0;
GLfloat y2=-0.7f;
int refreshMillis = 30;  
GLfloat xSpeed = 0.002f;      // Ball's speed in x and y directions
GLfloat ySpeed = 0.01f;
void initRendering()
{
    glEnable(GL_DEPTH_TEST);
}

void reshape(int w,int h)
{
    glViewport(0,0,w,h);

    glMatrixMode(GL_PROJECTION);

    glLoadIdentity();

  

}


void drawBall1()
{
    glColor3f(0.0,0.0,1.0);

    glPushMatrix();

    glTranslatef(x1,y1,0.0);

    glutSolidSphere(d,20,20);

    glPopMatrix();
}

void drawBall2(GLfloat *x2)
{

    glColor3f(1.0,0.0,.0);

    glPushMatrix();

    glTranslatef(*x2,y2,0.0);

    glutSolidSphere(d,20,20);

    glPopMatrix();

}

void update()
{

 x1 += xSpeed;
   y1 += ySpeed;

    if( y1>1.0)
        {
            ySpeed= -ySpeed;
        }
  if (y1<-1.0)

{
ySpeed= -ySpeed;
}
if (x1<-1.0)
{
xSpeed= -xSpeed;
}
if (x1>1.0)
{
xSpeed= -xSpeed;
}


}
void keyboard (unsigned char key, int x, int y )
{

GLfloat *x2;



switch (key) {
case 'd':
*x2= *x2+0.1f;
glutPostRedisplay();
break;
case 'a':
*x2= *x2-0.1f;
glutPostRedisplay();
break;
}
}



void display()
{
    glClear(GL_COLOR_BUFFER_BIT);

    glMatrixMode(GL_MODELVIEW);

    glLoadIdentity();

    //glShadeModel(GL_SMOOTH);
    drawBall1();
GLfloat *x2;

    drawBall2(x2); //niebieska

    update();

//colision

if((  y1-y2<d ) && (x1-*x2<d )&& (*x2-x1<d) )
{

ySpeed= -ySpeed;
}



    glutSwapBuffers();
}




void Timer(int value) {
   glutPostRedisplay();    // Post a paint request to activate display()
   glutTimerFunc(refreshMillis, Timer, 0); // subsequent timer call at milliseconds
}


int main(int argc,char **argv)
{
    glutInit(&argc,argv);

    glutInitDisplayMode(GLUT_DOUBLE);

    glutInitWindowSize(400,400);

    glutCreateWindow("gra Q");

  

    glutDisplayFunc(display);

   

    glutReshapeFunc(reshape);

  glutKeyboardFunc(keyboard);

glutTimerFunc(0, Timer, 0); 
 initRendering();
    glutMainLoop();

    return 0;
}

//to be continue..