substraction of time in computer programme?

Answer 1

What language?

in c# you can do it like this:

DateTime now = DateTime.Now;
DateTime then = DateTime.Parse("11/12/1950");
TimeSpan nst = now.Subtract(then);

TimeSpan has several properties that will give you the minutes, seconds, etc that would look like this:

nst.TotalSeconds
nst.TotalMinutes
etc

Answer 2

Depends on the program, but a lot will handle it well with just one date and time subtracted from another. Sometimes you have to take it to pieces a bit and fiddle with things. What is the language and what are you trying to do?