A countdown timer handy for many things.

boo.c

#include <stdio.h>
#include <time.h>

int main()
{
    time_t start, now;
    double secs = 0.0;
    int timercountdown = 10;

    start = now = time(NULL);

    while(1)
    {
        secs = difftime(now, start);

        if(secs > 1.0)
        {
            if(timercountdown > 0)
                printf("%d\n", timercountdown);

            start = now;

            timercountdown--;

            if(timercountdown == -1)
                break;
        }

        now = time(NULL);
    }

    puts("BOO! Gotcha!");

    return 0;
}