Algorithms - EdexcelUsing sequence, selection and iteration

Programs are designed using common building blocks. These building blocks, known as programming constructs, form the basis for all programs.

There are three basic building blocks to consider:

• sequence
• selection
• iteration

Sequence is the order in which instructions occur and are processed. Selection determines which path a program takes when it is running. Iteration is the repeated execution of a section of code when a program is running.

There are two types of iteration:

• count-controlled iteration
• condition-controlled iteration

All programs use one or more of these constructs. The longer and more complex the program, the more these constructs will be used repeatedly.

This guide uses pseudo-code examples to illustrate the constructs. It is important to realise that while all programming languages include these constructs, there may be slightly different formats.