Keskustelu: Ohjelmointikysymykset: C: Undefined reference to 'cos'

#include <stdlib.h>
#include <stdio.h>
#include <math.h>

/* COSWAVE.C - Generates a cosine wave: 8000 samples, 1 s, 200Hz	*/
/* (when played at 8000 samples/s), called cosine.dat		*/

int main()
{
    int length, status, i;
    short int *x;			/* a pointer to the array of samples */
    float freq;
    double arg, twopi;
    FILE *file_id;

    length = 8000;
    freq = 0.025;
    twopi = 8.0*atan(1.0);            	/* calculate 2*PI 	*/
    arg = twopi * freq;

/* allocate the sample array and set its cells to zero 		*/
    x = (short int *) calloc(length,sizeof(short int));
    if(!x) {
        printf("Unable to allocate space for samples\n");
        exit(1);
    }

/* Loop over the length of the array of samples 			*/
/* Luulen, etta hairio on tassa kohtaa                                  */
    for (i = 0 ; i < length ; i++)
        x[i] = (short int) 32000 * cos(i*arg);

    file_id = fopen("cosine.dat","wb");
    if(file_id == NULL) {
        printf("Unable to open file\n");
        exit(1);
    }
    status = fwrite(x,sizeof(short int),length,file_id);
    if(status < length) {
        printf("Unable to write all samples\n");
        exit(1);
    }
    fclose(file_id);
    return 0;
}