S3 SDD - selection statements

Selection statements

Python programming

​Decisions

Real life is full of examples of consequences which occur when you make a decision. For example if you fail to complete maths or computing homework you may be given a detention or the school may contact home.

Similarly if you complete homework regularly to a good standard you would likely receive a star or be nominated for pupil of the month in the department.

​Decisions in programming

A program can also make decisions and perform an action based around a condition being true. It can do this by using a selection statement. The words if and else are used to indicate which action should be performed in the event of a condition being true or false.

​Decisions in programming

All programming languages will support the use of slection statements, they are a commonly used construct.

​Decisions in programming

The following is an example of a simple IF... THEN ELSE... selection statement. it has been written in the SQA's reference language (this is a language which is similar to pseudocode).

Comparison operators

When coding selection statements in Python the following operators can be used:

​Operator	​Description
​==	Equal to​
​>	Greater than​
​<	Less than​
​>=	Greater than or equal to​
​<=	Less than or equal to​
​!=	Not equal to​

Comparison operators

When coding a selection statement, you must include the following:

Indentation - To indicate what line of code is run if a condition is met.

Colon - To indicate the beginning of a selection statement or loop.

Multiple Choice

Which of the following is used to indicate the beginning of a selection statement?

• semi-colon

• indentation

• hash tag

• colon