A-Level Computer Science - 11.2 Constructs

Objective: Use pseudocode to write a 'post-condition' loop

A post-condition loop is a type of loop where the condition is checked after the body of the loop has executed. This means the loop body always runs at least once, regardless of the initial value of the condition.

The general structure of a post-condition loop in pseudo-code is as follows:

1. Start with a variable initialization.
2. Begin a loop that continues as long as a condition is true.
3. Inside the loop, execute the loop body.
4. After the loop body has executed, check the condition.

Here's an example of a post-condition loop in pseudo-code, demonstrating a scenario where we want to repeatedly ask the user for input until a valid number is entered:

Example: Validating User Input

Step	Pseudo-code	Explanation
1. Initialize a variable	Declare a variable number as Integer.	This variable will store the user's input.
2. Start a loop	Begin a loop While number is not valid Display "Please enter a valid integer: " Read number from user End While	The loop continues until the user enters a valid integer.
3. Loop Body	Display "You entered: " + number // Perform operations with the valid number	Inside the loop, we display the entered number. You would typically perform other operations here.
4. Post-Condition	The loop terminates when number is valid.	This means the loop body has executed at least once.

Key characteristics of a post-condition loop:

• The loop body is guaranteed to execute at least once.
• The condition is checked after each iteration.

This type of loop is useful when you need to perform an action and then decide whether to repeat it based on the outcome of that action.