rotate a star in opengl (2D)
===

I have a 2D Star and i dont know how to rotate it around its center and also i dont know how to do it with a keyboard key. also i wanna ask is there any way to i make my object bigger or smaller with percent (cuz when i want to do it with changing pixels Star goes wrong)
Sorry for my English

this is my code:

    #include <GL/glut.h>
    #include <GL/gl.h>
    #include <GL/freeglut.h>
    
    void init (void)
    {
        glClearColor(0.0,0.0,0.0,00);
        glMatrixMode(GL_PROJECTION);
        gluOrtho2D(0.0,200.0,0.0,200.0);
    
    }
    void LineSegment(void)
    {
        glClear(GL_COLOR_BUFFER_BIT);
        glColor3f(1.0,1.0,1.0);
        glBegin(GL_LINE_LOOP);
        glVertex2i(20,120);
        glVertex2i(180,120);
        glVertex2i(45,20);
        glVertex2i(100,190);
        glVertex2i(155,20);
        glEnd();
        glFlush();
    }
    int main(int argc,char** argv)
    {
        glutInit(&argc,argv);
        glutInitDisplayMode(GLUT_SINGLE|GLUT_RGB);
        glutInitWindowPosition(50,100);
        glutCreateWindow("STAR");
        init();
        glutDisplayFunc(LineSegment);
        glutMainLoop();
        return 0;
    }