Program Logic and Design: Nested Loops

Definition and Usage

• Nested Loops: Loops within loops, where one loop (inner loop) is contained within another loop (outer loop).
• Purpose: Used when values of two or more variables repeat to produce every combination of values.

Syntax and Structure

• Some programming languages use curly braces to indicate nested loops (e.g., C++ and Java).
• Components:
  • Outer loop: contains the inner loop
  • Inner loop: contained within the outer loop

Example Process

1. Initialize the outer loop variable.
2. Test the outer loop variable.
3. Initialize the inner loop variable.
4. Test the inner loop variable.
5. Execute inner loop statements using outer and inner loop variables.
6. Alter the inner loop variable.
7. End the inner loop when the test is false.
8. Alter the outer loop variable.
9. Repeat until the outer loop variable test is false.

Key Points

• Inner loop must be completely contained within the outer loop.
• Each loop should have its separate counter.
• Control Counters: Used to control the number of iterations for each loop.
• Applications: Useful for handling spreadsheet-type data where the outer loop manages rows and the inner loop manages columns.

Detailed Example: Quiz Answer Sheets

• Goal: Use nested loops to create quiz answer sheets.
• Outer Loop: Controls parts 1, 2, 3, 4, 5.
• Inner Loop: Controls the questions within each part (e.g., question counters and lines).
• Termination Condition: When the quiz name is entered as 'zzz'.

Operational Steps

1. Input quiz name (initialization step).
2. Begin outer loop for parts (parts counter initialized and tested).
3. Within outer loop, begin inner loop for questions (question counter initialized and tested).
4. Output the part label and questions sequentially.
5. Alter question counter after each iteration of inner loop.
6. End inner loop after specified number of questions are outputted.
7. Alter part counter and repeat process for next part.
8. Continue looping until all parts and questions are processed, then prompt for new quiz name.
9. Exit program if 'zzz' is entered as quiz name.

Pseudocode Highlights

• Proper indentation is critical for avoiding logic errors.
• Alter control counters appropriately within loops.

Nested Loop Facts

• Inner loops are always entirely contained within outer loops.
• Inner loops complete all iterations for each single iteration of the outer loop.
• Total Iterations: Total iterations = (inner loop iterations) * (outer loop iterations). Example: 5 parts * 3 questions = 15 iterations.

Conclusion

• Nested loops are powerful tools for managing multi-dimensional data.
• Essential to maintain proper structure and control of loop counters.
• Join the next session to learn about avoiding common loop mistakes.