newbie prob with sqrt in c

Hi, I'm so new with c language, therefore this may be a fool one. Here's my code: #include #include main() { double x; x = 64.0; printf("kok : %f.\n", sqrt(x)); return 0; } In function `main': : undefined reference to `sqrt' collect2: ld returned 1 exit status Seems it can't find it in math.h; true? A grep showed me it's in tgmath.h instead.But including tgmath.h also didn't change anything. Thanks in advance..