implement time delay in c

In standard C (C99), you can use time() to do this, something like:

#include <time.h>
:
void waitFor (unsigned int secs) {
    unsigned int retTime = time(0) + secs;   // Get finishing time.
    while (time(0) < retTime);               // Loop until it arrives.
}

By the way, this assumes time() returns a 1-second resolution value. I don’t think that’s mandated by the standard so you may have to adjust for it.

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In order to clarify, this is the only way I’m aware of to do this with ISO C99 (and the question is tagged with nothing more than “C” which usually means portable solutions are desirable although, of course, vendor-specific solutions may still be given).

By all means, if you’re on a platform that provides a more efficient way, use it. As several comments have indicated, there may be specific problems with a tight loop like this, with regard to CPU usage and battery life.

Any decent time-slicing OS would be able to drop the dynamic priority of a task that continuously uses its full time slice but the battery power may be more problematic.

However C specifies nothing about the OS details in a hosted environment, and this answer is for ISO C and ISO C alone (so no use of sleep, select, Win32 API calls or anything like that).

And keep in mind that POSIX sleep can be interrupted by signals. If you are going to go down that path, you need to do something like:

int finishing = 0; // set finishing in signal handler 
                   // if you want to really stop.

void sleepWrapper (unsigned int secs) {
    unsigned int left = secs;
    while ((left > 0) && (!finishing)) // Don't continue if signal has
        left = sleep (left);           //   indicated exit needed.
}