How do you make a digital watch program in c?

Answer 1

I'm not going to write the code for you as it wouldn't be platform independent. However I will show you one possible technique using pseudocode.

Your program will essentially be an infinite loop. In pseudocode, you would use something similar to the following:

X = current_time (in seconds)

repeat

if X and current_time are equal

sleep for 500ms otherwise

let X = current_time

display X (in hours, minutes and seconds)

sleep for 250ms

It is important that your program go to sleep for a short period to reduce the number of comparisons it needs to make and thus reduce the processing time taken up by the program. How you achieve this depends on the operating system, but you cannot use a delay loop because this would consume valuable processing time by itself. In general, the sleep function should inform the operating system to put your program into an idle state for a set period of time. When the timer has elapsed, the OS will waken your program. Thus your program will spend the majority of its time in the idle state.

The sleep period should be less than a second, but must take into account the time it takes to perform the comparison and to display the results. In the code above, the program will sleep for 1/2 a second when there is no change, and 1/4 a second when there is a change. The periods can be adjusted to improve the accuracy of the watch; if they're too high, the clock may periodically jump a second, but too low and the program takes up valuable processing time doing nothing besides checking the current time.

If you're only interested in hours and minutes, then both sleep periods can be increased up to 30 seconds, but for accuracy within a second or so, sleep for 1000ms.