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====== Control Structures: Repetition in Algorithms ======

Mithat Konar\\ 
2019-02-11

===== Introduction =====

  * Counter control
  * Sentinel/flag control
  * Input validation
  * Menus
  * Iterators

===== Counter-controlled repetition =====
  * "Repeat something a known number of times."
  * Uses a counter variable.
  * Pseudocode:<code>Set counter's initial value
While counter has not yet exceeded the STOP_VALUE
    Do something
    Increment counter</code>

===== Sentinel control =====

  * **Sentinel**:
    * Value(s) that indicate(s) a special condition --- a "special value"

===== Sentinel-controlled repetition =====
  * "Repeat as long as a sentinel condition is not matched."
  * Pseudocode:<code>Get value
While value is not SENTINEL value
    Do something
    Get value</code>
  * Input validation might be considered a special case of sentinel controlled repetition.
  * **Flag**:
    * Sometimes used as a synonym for sentinel
    * Sometimes means a sentinel that is a Boolean value

===== Input validation =====
    * "Prevent moving to next section until user has entered valid data."
    * Pseudocode:<code>Get input value from user
While input value is not valid
    Get input value from user</code>

===== Menus =====
  * Repeating menus can be implemented with sentinel control.
  * Pseudocode:<code>Show menu
Get menu choice from user
While input value is not QUIT value
    Process the menu choice
    Show menu
    Get menu choice from user</code>

===== Iterators =====
  * Do something to every item in a collection.
  * Pseudocode:<code>For each item in collection
    Do something with or to the item</code>