Xcode build failed due to undefined symbols

Question

I'm trying to build a lighting model program in Xcode but it keeps saying build failed due to undefined symbols, but I don't understand how to fix it. My code is below.

#include <GLUT/glut.h>
#include <stdlib.h>

static GLfloat shift = 0.0;   // Initialize the fourth parameter of the plane equation

void init(void)
{
    glClearColor (0.0, 0.5, 0.0, 0.0);
    glEnable (GL_LIGHTING);
    glEnable (GL_LIGHT0);
    glEnable (GL_DEPTH_TEST);
}
    
void display (void)
{
    glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    GLdouble eqn0[4] = {1.0, 0.0, 0.0, shift};  // Parameters array of the first plane
    glClipPlane (GL_CLIP_PLANE0, eqn0);         // Create the first plane with eqn0 array
//    glEnable (GL_CLIP_PLANE0);                  // Activate the first plane

/* Draw five different objects at different locations  */
    glLineWidth(2.0);
    glPushMatrix();
      glutSolidTeapot (2.0);
      glTranslatef (3.0, 3.0, 0.0);
      glutSolidTorus (0.4, 0.8, 20, 20);
      glTranslatef (-6.0, 0.0, 0.0);
      glutWireIcosahedron ();
      glTranslatef (0.0, -6.0, 0.0);
      glutSolidSphere (1.0, 20, 20);
      glTranslatef (6.0, 0.0, 0.0);
      glutWireCube (2.0);
    glPopMatrix();
    glutSwapBuffers ();
}

void reshape(int w, int h)
{
    glViewport (0, 0, (GLsizei) w, (GLsizei) h);
    glMatrixMode (GL_PROJECTION);
    glLoadIdentity ();
    gluPerspective (60.0, (GLfloat) w/(GLfloat) h, 1.0, 20.0);
    glMatrixMode (GL_MODELVIEW);
    glLoadIdentity ();
    gluLookAt (0.0,0.0,10.0, 0.0,0.0,0.0, 0.0,1.0,0.0);
}


/* Implement any keyboard function to increase or decrese the value of
"shift" to interactively adjust the position of the clipping plane */

void keyboard (unsigned char key, int x, int y)
{
    switch (key) {
        case 'f':
//          shift =
        glutPostRedisplay ();
            break;
        case 27:
            exit(0);
            break;
        default:
            break;
    }
}

int main(int argc, char** argv)
{
    glutInit (&argc, argv);
    glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
    glutInitWindowSize (800, 800);
    glutInitWindowPosition (100, 100);
    glutCreateWindow ("Planner clipping");
    init ();
    glutDisplayFunc (display);
    glutReshapeFunc (reshape);
    glutKeyboardFunc (keyboard);
    glutMainLoop();
    return 0;
}

I need a screen to pop up with a green background and a gray teapot.

Below are the errors that keep occurring:

Showing Recent Issues

Build target lightPA2 of project lightPA2 with configuration Debug


Undefined symbols for architecture x86_64:
  "_glClear", referenced from:
      display() in main.o
  "_glClearColor", referenced from:
      init() in main.o
  "_glClipPlane", referenced from:
      display() in main.o
  "_glEnable", referenced from:
      init() in main.o
  "_glLineWidth", referenced from:
      display() in main.o
  "_glLoadIdentity", referenced from:
      reshape(int, int) in main.o
  "_glMatrixMode", referenced from:
      reshape(int, int) in main.o
  "_glPopMatrix", referenced from:
      display() in main.o
  "_glPushMatrix", referenced from:
      display() in main.o
  "_glTranslatef", referenced from:
      display() in main.o
  "_glViewport", referenced from:
      reshape(int, int) in main.o
  "_gluLookAt", referenced from:
      reshape(int, int) in main.o
  "_gluPerspective", referenced from:
      reshape(int, int) in main.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)