Difference between revisions of "Loops"

Revision as of 22:16, 6 March 2007

An Introduction

A loop is a control structure that repeatedly executes a sequence of steps for as long as a test condition evaluates to true. What does iterate mean?

(Another definition less informal?)

A loop is a control structure that allows you to repeat the same sequence of code for any given time.

Until now all your programs have been working from top to bottom. Imagine if you were to write a game to guess a secret number from 1 to 100. The entire program would consist of one hundred if statements to account for each turn to check and see if the number chosen is correct.

Types of Loops

• while
• for -Roger
• nested loops -Roger

Test Condition

Loops use the test condition to decide whether or not to enter the body of the loop.

Scope

Everything within the body of the loop is considered to be in the scope of the loop. In the case of a for loop, any variable declared in the inializer is considered to be within the scope of the loop. Declaring a variable within the variable within the scope of a loop is highly discouraged. This variable would be difined again everything time the loop iterates, causing a significant waste of memory.

Infinite Loops

An infinite loop is any loop that continues to repeat forever. There are situations where this is useful, but if you didn't intentionally program it in, then it causes a fatal error for your program. These occur if the test condition in your loop will never be false. Here are a few examples of infinite loops:

while(true) //always true
{
}
------------------------------------------------
for(int i = 0; i < 20; i++) //counter reset to 0 every time
{
    i = 0;
}
------------------------------------------------
for(int i = 0; i < 5e9; i++) //integers can't be as big as 5e9(5*10^9), so i will overflow to negative
{
}

Additional Information

• Multiple Control Statements
• The Evil Do-While Loop
• Running Totals and Sentinel Values

Review Questions and Exercises

Here you will find some Review Questions and Exercises to help you understand and and learn to use loops.