Call function periodically without using threads and sleep() method in c

Question

I want to call a function, lets say every 10 or 20 seconds. When I searched, I came up with threads and sleep() method everywhere.

I also checked for time

Answer 1

A naive solution would be something like this:

/* Infinite loop */
time_t start_time = time(NULL);
for (;;)
{
    time_t now = time(NULL);

    time_t diff = now - start_time;

    if ((diff % 10) == 0)
    {
        /* Ten seconds has passed */
    }

    if ((diff % 20) == 0)
    {
        /* Twenty seconds has passed */
    }
}

You might want a flag that tells if the function has been called, or it will be called several times during the single second (diff % 10) == 0 is true.