Monday, October 2, 2006

Repetition  (while, do-while, and for statements) Repetition is also called "Iteration"

Topics

• Loops are if statements that automatically repeat.
• The syntax of the while loop, simply change the "if" to "while" and it will repeat.
• The concept of a control variable.  Almost always the control variable will be in the condition, inside the parentheses.
• The three programming steps you must do to create a working loop:
•     1. Initialize the control variable before the loop
•     2. Test the control variable inside the condition
•     3. Update the control variable inside the loop
• Infinite loops are usually the result of not updating the control variable inside the loop.

• Counter Controlled Loops
•     Used when the program knows how many times the loop must execute
•     The control variable is usually a simple integer counter.
•     for loops as a alternative syntax to the while loops
•     for loops are usually the best way to write counter controlled loops.
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• Event Controlled Loops
•     Used when the number of times the loop must execute can not be predicted
•     The control variable is usually inputted from the user.
•     while loops or do-while loops (see below) are usually the best way to write event controlled loops.
•    
• Pretest and posttest loops
•     while loops are pretest loops
•         in pretest loops the initialization of the control variable usually occurs before the beginning of the loop
•     do-while loops are post test loops
•         in a do-while loop, the initialization of the control variable usually occurs inside the loop
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• Alternative ways to terminate a loop (should be rarely, and carefully, used)
•     the break statement
•     the continue statement
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• Highly discouraged:
•     using a return statement inside a loop
• Nested loops -- two dimensional problems
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• if statements inside of loops -- doing a test over and over
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• while statements inside of an if statement -- deciding whether a loop should execute        

Practice Problems

Repetition Practice Problems -- do these in preparation for the third test.

Readings

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