I want to continuously rotate 2 spheres, however the rotation does not seem to work.

Here is my code:

float angle = 0.0f;

void light(){
    glEnable(GL_LIGHTING);
    glEnable(GL_LIGHT0);
    glEnable(GL_LIGHT1);

    // Create light components
    GLfloat positionlight1[] = { 9.0, 5.0, 1.0, 0.0 };
    GLfloat positionlight2[] = {0.2,2.5,1.3,0.0};
    GLfloat light_ambient1[] = { 0.0, 0.0, 1.0, 1.0};
    GLfloat light_diffuse[] = { 1.0, 1.0, 1.0, 1.0 };

    glLightfv(GL_LIGHT0, GL_AMBIENT, light_ambient1);
    glLightfv(GL_LIGHT1, GL_DIFFUSE, light_diffuse);
    glLightfv(GL_LIGHT0, GL_POSITION, positionlight1);
    glLightfv(GL_LIGHT1, GL_POSITION, positionlight2);

}

void changeSize(int w, int h) {

    if (h==0) // Prevent A Divide By Zero By
    {
        h=1; // Making Height Equal One
    }

    glMatrixMode(GL_PROJECTION); // Select The Projection Matrix
    glLoadIdentity(); // Reset The Projection Matrix
    glViewport(0,0,w,h);// Reset The Current Viewport
    // Calculate The Aspect Ratio Of The Window
    gluPerspective(45.0f,(GLfloat)w/(GLfloat)h,0.1f,100.0f);

    glMatrixMode(GL_MODELVIEW); // Select The Modelview Matrix // Reset The Modelview Matrix
}


void renderScene(void) {

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);


    glPushMatrix(); //set where to start the current object

    glTranslatef(0.0,1.2,-6);
    glRotatef(angle,0,1.2,-6);
    glutSolidSphere(1,50,50);

    glPopMatrix(); //end the current object transformations
    glPushMatrix(); //set where to start the current object

    glTranslatef(0.0,-2,-6);
    glRotatef(angle,0,-2,-6);
    glutSolidSphere(0.5,50,50);

    glPopMatrix(); //end the current object transformations 

    angle=+0.1;
    glutSwapBuffers();
}


int main(int argc, char **argv) {

    // init GLUT and create window
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA);
    glutInitWindowPosition(100,100);
    glutInitWindowSize(500,500);
    glutCreateWindow("Hello World");
    // register callbacks
    light();
    glutDisplayFunc(renderScene);
    glutReshapeFunc(changeSize);
    glutIdleFunc(renderScene);

    // enter GLUT event processing loop
    glutMainLoop();

    return 1;
}

Graphicstest::Graphicstest(void)
{
}

In the renderscene where i draw,translate and rotate my 2 spheres. It does not seem to rotate the spheres continuously. What am i doing wrong?