Program Logic and Design: Common Loop Applications

Introduction to Loops

• Loops are commonly used for:
  • Accumulating totals
  • Validating data
• Examples include:
  • Business reports with totals
  • List of real estate sales and their total value
• Building a running total as we go in our loop using a cumulative variable

Accumulators

• Accumulator: Gathers values or totals
  • Similar to a counter, but increments by a specific value
• Steps for using an accumulator:
  1. Initialize to zero
  2. Alter once for every data set processed
  3. Output at the end of processing

Example: Monthly Sales Report

• Task: Sum prices and generate a total
• Method: createReport
  • Initialize accumulatedPrice to 0
  • For each address, add the price to accumulatedPrice
  • Outputs a summary with accumulated prices
• Process: Playing computer
  • Start with accumulator at 0
  • Add each address's price sequentially
  • Update and store new accumulated price each iteration

Data Validation with Loops

• Validate data to ensure it falls within an acceptable range
• Defensive Programming: Prepare for all possible errors
  • Example: Reject invalid month numbers (e.g., less than 1 or greater than 12)
  • Use loops to re-prompt for valid input
• GIGO (Garbage In, Garbage Out): Invalid input leads to invalid output

Example: Validating Birth Month Input

• Use if statements to check validity
• Use loops for multiple re-prompts
• Limit iterations to avoid user frustration:
  • Give a fixed number of attempts (e.g., 3 chances)
  • Force a default value if invalid input persists

Validating Data Types

• Ensure correct data type (e.g., numbers instead of strings)
• Use built-in methods like isNumeric
  • Check validity and prompt user if invalid
  • Use loops to give multiple attempts
  • Force a default value after fixed attempts

Example: Validating Salary Input

• Check if input is numeric
• Re-prompt user if not numeric
• Limit attempts and force a default value if necessary

Conclusion

• Use loops to:
  • Validate data
  • Ensure reasonableness and consistency
• Makes programs more user-friendly
• Next topic: Comparing selections and loops