W1154 For Loop

Within these castle walls be forged Mavens of Computer Science ...

— Merlin, The Coder

Roller Coaster Loop

Prerequisites

• W1151 Conditional and Flow Chart

Introduction

Loops are the general term for executing a defined segment of code zero or more times, where the number of iterations is dependent upon test conditions within the loop. The for loop is a construct which enables us to execute a segment of code a defined number of times. It is thus the most appropriate choice when we know in advance how to calculate the number of iterations prior to beginning the loop. While this construct is not strictly necessary, it provides syntactic sugar by clarifying intent.

General Loop

General Loop

In the case of a general loop, we can see that the three statements in the figure on the right will be repeated. However, without a test condition this loop would theoretically execute forever and is formally termed an infinite loop. To be useful, a test condition is required in order to inform the CPU when the loop should be exited. Thus, loops generally have two distinct parts:

• A test condition which informs the CPU when the loop should be exited
• A body which is the code which is repeated for each iteration of the loop