A subroutine is a collection of statements which perform a specific task. Subroutines may be written in the C programming language or in the Quantum language. Each subroutine must have a unique name by which it can be called up when required.

Subroutines can be used to make your program more readable by eliminating the need to use go tos in certain circumstances. If you use a subroutine with a name describing its purpose it will be immediately apparent what is to be done, and it will mean you don’t have to go skipping backwards and forwards in the program in order to understand what it is doing.