Chapter 7: The Repetition Structure

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Chapter 7The Repetition Structure

• Introduction to Programming with C
• Fourth Edition

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Objectives

• Include a repetition structure in pseudocode and
  in a flowchart
• Code a pretest loop using the C while statement
• Initialize and update counters and accumulators
• Code a pretest loop using the C for statement

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Using the Repetition Structure

• Repetition structure or loop - allows repeated
  processing of one or more program instructions
  until some condition is met
• Repetition structure can be either a pretest loop
  or a posttest loop
• Pretest loop evaluation occurs before loop
  instructions are processed
• Posttest loop evaluation occurs after loop
  instructions are processed

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Pretest Loops
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Pretest Loops (continued)
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Pretest Loops (continued)

• Every loop has
• a loop condition
• a loop body
• Loop body
• instructions within a loop
• Loop condition
• appears at the beginning of a pretest loop
• determines the number of times instructions
  within the loop are processed

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Pretest Loops (continued)

• Sentinel value special value to end the loop
• Priming read
• Appears above the loop
• Used to prepare or set up the loop

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Components of a Loop
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ODonnell Incorporated Algorithm Shown in
Flowchart Form
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Using the while Statement to Code the Pretest Loop

• While statement programmer must supply the loop
  condition to be evaluated
• Loop condition
• must be a Boolean expression (true or false)
• can contain variables, constants, functions,
  methods, arithmetic operators, comparison
  operators, and logical operators
• Endless or infinite loop one that processes its
  instructions indefinitely

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Syntax of the C while Statement
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Using Counters and Accumulators

• Counter - a numeric variable used for counting
• Accumulator - a numeric variable used for
  accumulating a value
• Initializing - assigning a beginning value to the
  counter or accumulator
• Updating or incrementing - adding a number to the
  value stored in the counter or the accumulator

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Counter-Controlled Pretest Loops
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Using the for Statement to Code a Pretest Loop

• Most common use for the for statement
• Code pretest loops whose processing is controlled
  by a counter
• For statement
• Begins with the for clause
• Followed by the body of the loop
• If the loop body contains more than one
  statement
• Statements must be entered as a statement block
  i.e., enclosed in braces ()

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Syntax of the C for statement
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for Statement Displays the Numbers 1 Through 3
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for Statement Calculates and Displays a Commission
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for Statement Calculates and Displays a Bonus
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Summary

• Repetition structure or loop - allows repeated
  processing of one or more program instructions
  until some condition is met
• Repetition structures contain a condition and a
  loop body