The title says it all.

What is the difference between a Function and a Procedure?

When should I use which?


2 Answers 2


According to algpseudocode, these two are structurally the same, apart from their name:

   [2]{\algorithmicprocedure\ \textproc{#1}\ifthenelse{\equal{#2}{}}{}{(#2)}}%
   {\algorithmicend\ \algorithmicprocedure}%
   [2]{\algorithmicfunction\ \textproc{#1}\ifthenelse{\equal{#2}{}}{}{(#2)}}%
   {\algorithmicend\ \algorithmicfunction}%

From a programming perspective, the difference is embedded in the language and have the following commonly-used structure (in laymen's terms):

  • Procedure: A collection of instructions
  • Function: A collection of instructions that also returns something

A minimal example indicating their typical usage:

enter image description here

\usepackage{algpseudocode}% http://ctan.org/pkg/algorithmicx
  \State body
  \State body
  \State \Return something
  • should we specify the output of Function somewhere or it is just specified through return?
    – Ahmad
    Commented Jul 9, 2016 at 6:37
  • Is it the standard, if we mention both input and output parameters in {params} Commented Sep 17, 2017 at 1:23
  • @RenjthVRavi: That depends. This is pseudo-code, so as long as it's clear in the presentation.
    – Werner
    Commented Sep 17, 2017 at 17:17
  • A function, depending on definition, also does not modify state (has side-effects). Commented Nov 21, 2018 at 19:36

This is not at all a TeX-related question, but a function returns a value while a procedure does not (void in C++). A procedure only performs some actions, it is invoked because of its side effects.

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