How to program a problem that needs the difference of time..? example,the sorting started at 10:15 and ends at 10:30.so the difference time in order the numbers to be sorted is 15min..

This depends more on how time is stored then a C++ function. Since C++ doesn't have a native data store, you have to take that into account. If the data is stored as a text string, then you need to parse out the time values. Many databases store date/time values as numbers. For example, Access and SQL Server store them as a double precision number where the integer portion represents the number of days from a base date and the time is represented as a fraftin of a 24 hour day.