Go4Expert - what does this error mean ?

hello all ,
I am new to C programming and trying to learn by working some online tutorials.
I am working on a linux OS ( Ubuntu ) .

so the program is to calculate a table of sine values and I typed in the code pretty much the way it was show in the tutorial, the code is shown below:

Code:

                                /* Written: Winter 1995        */

#include < stdio.h>

#include < math.h>



void main()

{

    int    angle_degree;

    double angle_radian, pi, value;



                                        /* Print a header */

    printf ("\nCompute a table of the sine function\n\n");



                                        /* obtain pi once for all */

                                        /* or just use pi = M_PI, where

                                           M_PI is defined in math.h         */

    pi = 4.0*atan(1.0);

    printf ( " Value of PI = %f \n\n", pi );



    printf ( " angle     Sine \n" );



    angle_degree=0;                        /* initial angle value                  */

                                        /* scan over angle                  */



    while (  angle_degree <= 360 )        /* loop until angle_degree > 360 */

    {

       angle_radian = pi * angle_degree/180.0 ;

       value = sin(angle_radian);

       printf ( " %3d      %f \n ", angle_degree, value );



       angle_degree = angle_degree + 10; /* increment the loop index         */

    }

}

When I try to complile the program by typing

$ gcc program_name.c

I get the following error :

/tmp/cciKZE0g.o: In function `main':
sine.c:(.text+0x58): undefined reference to `sin'
collect2: ld returned 1 exit status

what does this mean ?? what should I do ? can any one help ?

thanks ,
raurava