Standard C (or C++) doesn't have any sound functions. You can try printf("\a"); This might give you a beep sound.
If you are using windows you can use Beep function if you include <windows.h> I think. Beep(440, 500); 440 is the frequency of the sound in hertz and 500 is the duration of the sound in milliseconds.
If you are using a different OS or want something more platform independent you need to use an external library like SDL, OpenAL or FMOD.
eh, you could just beep at different intervals with different frequencies. I split 500ms into 4 increments of 125ms long beeps and made a reasonable tone for a timer I wrote. It turns out that it's pretty nice. ^^