Compiling and runnin OpenGL (glut) program in ubuntu 10.10

I wrote this code:

#include <stdio.h>
#include <stdlib.h>
#include <GL/glx.h>    
#include <GL/gl.h>
#include <GL/glut.h>


void init()
{
    glClearColor(1.0,1.0,1.0,0.0);
    glMatrixMode(GL_PROJECTION);
    gluOrtho2D(0.0,200.0,0.0,150.0);
 }

 void lineSegment()
 {
    glClear(GL_COLOR_BUFFER_BIT);
    glColor3f(0.0,0.0,1.0);
        glBegin(GL_TRIANGLES);
            glVertex2i(40,120);
            glVertex2i(40,20);
            glVertex2i(80,20);
        glEnd();
    glFlush();
 }
 int main()
 {
    glutInitDisplayMode(GLUT_SINGLE|GLUT_RGB);
    glutInitWindowPosition(50,100);
    glutInitWindowSize(400,300);
    glutCreateWindow("An Example OpenGL....");
    init();
    glutDisplayFunc(lineSegment);
    glutMainLoop();
    return 0;
 }

and this is my error.

funfullson@funfullson:~$ gcc gl.cpp 
/tmp/cchfRGT2.o: In function `init()':
gl.cpp:(.text+0x2a): undefined reference to `glClearColor'
gl.cpp:(.text+0x36): undefined reference to `glMatrixMode'
gl.cpp:(.text+0x5a): undefined reference to `gluOrtho2D'
/tmp/cchfRGT2.o: In function `lineSegment()':
gl.cpp:(.text+0x6e): undefined reference to `glClear'
gl.cpp:(.text+0x8d): undefined reference to `glColor3f'
gl.cpp:(.text+0x99): undefined reference to `glBegin'
gl.cpp:(.text+0xad): undefined reference to `glVertex2i'
gl.cpp:(.text+0xc1): undefined reference to `glVertex2i'
gl.cpp:(.text+0xd5): undefined reference to `glVertex2i'
gl.cpp:(.text+0xda): undefined reference to `glEnd'
gl.cpp:(.text+0xdf): undefined reference to `glFlush'
/tmp/cchfRGT2.o: In function `main':
gl.cpp:(.text+0xf6): undefined reference to `glutInitDisplayMode'
gl.cpp:(.text+0x10a): undefined reference to `glutInitWindowPosition'
gl.cpp:(.text+0x11e): undefined reference to `glutInitWindowSize'
gl.cpp:(.text+0x12a): undefined reference to `glutCreateWindow'
gl.cpp:(.text+0x13b): undefined reference to `glutDisplayFunc'
gl.cpp:(.text+0x140): undefined refere