画出一个五角星

#include <glut.h>
#include <math.h>
const int n = 5;
const GLfloat R = 0.5f;
const GLfloat Pi = 3.1415926536f;

void myDisplay(void) {
    GLfloat a = 1 / (2 - 2 * cos(72 * Pi / 180));
    GLfloat bx = a * cos(18 * Pi / 180);
    GLfloat by = a * sin(18 * Pi / 180);
    GLfloat cy = -a * cos(18 * Pi / 180);
    GLfloat PointA[2] = { 0, a }, PointB[2] = { bx, by }, PointC[2] = { 0.5, cy }, PointD[2] = { -0.5, cy }, PointE[2] = { -bx, by };
    glClear(GL_COLOR_BUFFER_BIT);
    glBegin(GL_LINE_LOOP);
    glVertex2fv(PointA);
    glVertex2fv(PointC);
    glVertex2fv(PointE);
    glVertex2fv(PointB);
    glVertex2fv(PointD);
    glEnd();

    glFlush();
}

int main(int argc, char *argv[]){
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE);
    glutInitWindowPosition(10, 10);
    glutInitWindowSize(400, 400);
    glutCreateWindow("the first opengl program");
    glutDisplayFunc(&myDisplay);
    glutMainLoop();
    return 0;
}