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:
Set counter's initial value While counter has not yet exceeded the STOP_VALUE Do something Increment counter
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:
Get value While value is not SENTINEL value Do something Get value - 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:
Get input value from user While input value is not valid Get input value from user
Menus
- Repeating menus can be implemented with sentinel control.
- Pseudocode:
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
Iterators
- Do something to every item in a collection.
- Pseudocode:
For each item in collection Do something with or to the item