OPENGL PROGRAM TO DISPLAY SINC FUNCTION

#include<GL/glut.h>
#include<stdlib.h>
#include<math.h>

const int screenWidth=640;
const int screenHeight=480;


void myInit()
{
     glClearColor(0.0,0.0,0.0,0.0);
     glColor3f(1.0,0.0,0.0);
     glPointSize(3.0);
     //glMatrixMode(GL_PROJECTION);
     //glLoadIdentity();
     //gluOrtho2D(0.0,(GLdouble)screenWidth,0.0,(GLdouble)screenHeight);
    
     }
    
     //set window
     void setWindow(float left,float right,float bottom,float top)
     {
          glMatrixMode(GL_PROJECTION);
          glLoadIdentity();
          gluOrtho2D(left,right,bottom,top);
          }
         
          //set view port
          void setViewport(int left,int right,int bottom,int top)
          {
               glViewport(left,right,bottom,top);
               }
    
     void myDisplay()
     {
          GLdouble i=0;
          GLfloat x=0;
          glClear(GL_COLOR_BUFFER_BIT);
          setWindow(-4.0,4.0,-0.3,1.0);
          //setViewport(640,0,480,0);
          glBegin(GL_POINTS);
          for(x=-4.0;x<4.0;x+=0.1)
          glVertex2f(x,sin(3.1415*x)/(3.1415*x));
         
          glEnd();
         
         
          glColor3f(0.0,1.0,0.0);
          glBegin(GL_LINE_STRIP);
          glVertex2i(320,480);
          glVertex2i(320,0);
          glEnd();
         
          glFlush();
          }
                                 
                                                   
                                                   
                                                   
    
    
     int main(int argc, char **argv)
     {
         glutInit(&argc,argv);
         glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
         glutInitWindowSize(640,480);
         glutCreateWindow("sinc function = sin(PI*X)/PI*X");
         glutDisplayFunc(myDisplay);
      
         myInit();
        
         glutMainLoop();
         }