Structured program theorem

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The structured program theorem is a theorem in programming and computer science. A computer program can be split into pieces of code that do a certain task. According to the structured program theorem, these smaller tasks can be combined in only three ways to get any larger task done.

A program gets a large task done by splitting it into many smaller tasks that the computer can do easily. These smaller tasks are called subprograms in computer science. According to the structured program theorem, the three ways subprograms can be combined are:

  1. In sequence. Executing (running) one subprogram, and then executing another subprogram.
  2. By selection. Executing a subprogram based on a certain condition.
  3. In repetition. Executing the same subprogram over and over again.

The theorem was first published in 1966 by Corrado Böhm and Guiseppe Jacopini. It comes from the 1946 description of the von Neumann architecture and the normal form theorem developed by Stephen Kleene.