3.8 Iteration

1. Exam Points

• Iterations:
  • REPEAT x TIMES
  • REPEAT UNTIL(EXPRESSION)
• Nested iterations
• Use natural language to describe an algorithm with iterations.
• Use of iterations:
  • Select the right algorithm for a given problem.
  • Predict result or output of given code segments.
  • Compare two iteration algorithms.
  • Represent iterations using flow charts.

2. Knowledge Points

(1) Iteration

• Iteration is a repeating portion of an algorithm.
• Iteration repeats a specified number of times or until a given stopping condition is met.
• Iteration constructs (构造/结构)
  • repeat n times
    • Syntax
      
    • Example
      
  • repeat until(exit condition)
    • Syntax
      
    • Example
      
• In REPEAT UNTIL(condition) iteration, an infinite loop occurs when the ending condition will never evaluate to true.
  • Example:
    
• In REPEAT UNTIL(condition) iteration, if the conditional evaluates to true initially, the loop body is not executed at all, due to the condition being checked before the loop.
• An iteration can be nested within another, you can nest any of the following loop inside another loop.
  • repeat n times
  • repeat until(condition)
• Example of nested iteration:
  
• Note: Remember to update the loop control variable to avoid infinite loops.

3. Exercises

• Practice
• Solution