# Choice

One of the essential properties of a computer program is its ability to modify its actions depending on its circumstances and environment. In other words, its behaviour is not predetermined, but can vary from one execution to another. In this chapter, we shall introduce a new plain mode, describe the operators using or yielding values of the new mode, and then investigate the program structures which allow an Algol 68 program to choose between alternatives.

Subsections

- Boolean values
- Boolean operators
- Relational operators
  - Exercises
- Compound Boolean formulæ
  - Exercises
- Conditional clauses
  - Pseudo-operators
  - Exercises
- Multiple choice
  - Exercises
- Summary
  - Exercises