Using Loop Control Variables

Overview

• Discussing the concept and use of loop control variables in loop structures.
• Loop control variable: A condition to control the number of repetitions in a loop.

Steps to Control Loop Repetitions

1. Initialize Loop Control Variable: Before entering the loop.
2. Test Control Variable: Done in the condition of the loop.
3. Alter Control Variable: Modify in the loop body.

Types of Loops

1. Definite Loop

• Executes a predetermined number of times.
• Counter-controlled loop: Programm counts loop repetitions.
• Alter by incrementing or decrementing (typically by 1).
• Example of Counter:
  • Initialize count to 0.
  • Evaluate if Count is less than a specified number.
  • Increment count after executing the loop body.
  • Example provided in lecture outputs "hello" four times.

2. Infinite Loop

• When the program endlessly runs the loop.
• Strategies to avoid: Proper initialization, testing, and alteration.

3. Indefinite Loop

• Uses Sentinel value (user decides the number of repetitions).
• Example:
  • User is prompted to continue or stop the loop.
  • Loop control variable is modified based on user input.

Strategy for Proper Loops

1. Starting Value: Provide an initial value for control variable.
2. Testing the Loop Variable: Check meaningful conditions to determine repetitions.
3. Altering Control Variable: Update the count to keep track of iterations.

Example: Payroll Program

• Sentinel value in the form of a name.
• Loop until a specific quit condition (e.g., xxx).

Conclusion

• Key points covered: Loop control variables, definite loops, infinite loops, and indefinite loops.
• Next topic: Nested loops.