opengl program to display "sinc function"

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

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

GLdouble a=0,b=0,c=0,d=0;

void myInit()
{
     glClearColor(1.0,1.0,1.0,0.0);
     glColor3f(1.0,0.0,0.0);
     glPointSize(3.0);
     glMatrixMode(GL_PROJECTION);
     glLoadIdentity();
     gluOrtho2D(0.0,(GLdouble)screenWidth,0.0,(GLdouble)screenHeight);
     a=100;
     b=0.0;
     c=d=100;
    
     }
    
     void myDisplay()
     {
          GLdouble i=0;
          glClear(GL_COLOR_BUFFER_BIT);
          glBegin(GL_POINTS);
                            
                                       for(i=0;i<3.5;i+=0.005)
                                       {
                                                    GLdouble func=exp(-i)*cos(2*3.14159*i);
                                                    glVertex2i(a*i+b,c*func+d);
                                                    }
                                                    glEnd();
                                                   
                                                    glBegin(GL_LINES);
                                                    glColor3f(0.0,0.0,1.0);
                                                    glVertex2i(0.0,screenHeight/2);
                                                    glVertex2i(screenWidth,screenHeight/2);
                                                    glEnd();
                                                   
                                                    //to test
                                                    glColor3f(0.0,1.0,0.0);
                                                    glBegin(GL_POINTS);
                                                    glVertex2i(68,48);
                                                    glEnd();
                                                   
                                                    glFlush();
                                                    }
                                                   
                                                   
                                                   
    
    
     int main(int argc, char **argv)
     {
         glutInit(&argc,argv);
         glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
         glutInitWindowSize(640,480);
         glutCreateWindow("exponential plot");
         glutDisplayFunc(myDisplay);
      
         myInit();
        
         glutMainLoop();
         }