2-Repetition-Structure

Lesson Title

• Manuel S. Enverga University Foundation, Lucena City

• Autonomous University College of Engineering

• Instructor: Hannah Shamira P. Santonil

Learning Outcomes

• Introduction to Repetition Structures

• The while Loop: A Condition-Controlled Loop

• The for Loop: A Count-Controlled Loop

• Sentinels

• Input Validation Loops

• Nested Loops

Introduction to Repetition Structures

• Definition: A repetition structure (loop) is used to execute a statement or set of statements repeatedly.

• Purpose: It reduces the need for repetitive code, allowing for cleaner and more efficient programming.

• Key Concept: Instead of writing the same operations multiple times, code can be encapsulated within a loop that performs the task whenever necessary.

Types of Repetition Structures

Condition-Controlled Loops

• Description: Utilizes a true/false condition to dictate repetitions.

• Example: while loop in Python.

Count-Controlled Loops

• Description: Repeats a specified number of times.

• Example: for loop in Python.

The while Loop: A Condition-Controlled Loop

• Concept: Executes as long as a condition is true.

• Parts of the Loop:

  • Condition: Tested for true/false.

  • Execution: Statements repeat while condition is true.

General Syntax of the while Loop

while condition:
    statement
    statement
    ...

Example of while Loop: Commission Calculation

Program 4-1 (commission.py)

1. Initialize loop control variable: keep_going = 'y'

2. Begin while loop: while keep_going == 'y':

   • Input sales and commission rate from user.

   • Calculate commission.

   • Display commission.

   • Ask user if they want to calculate another commission.

3. Example Output: Displays commission calculations based on user input.

4. Notes: The loop terminates when keep_going is not 'y'.

The while Loop: Pretest Loop

• Definition: Condition is evaluated before the loop executes.

• Implication: Certain initial steps may need to be performed to ensure at least one iteration occurs.

Example of while Loop: Temperature Control

Program 4-2 (temperature.py)

• Scenario: Monitor the temperature of a substance.

1. Get initial temperature from user.

2. If it exceeds a threshold, implement specific actions repeatedly until acceptable temperature.

3. Display results based on user-defined temperature inputs.

The for Loop: A Count-Controlled Loop

• Definition: Iterates a specified number of times using a sequence.

• General Syntax:

for variable in [value1, value2, ...]:
    statement
    ...

Using the range Function with the for Loop

• Purpose: Simplifies creating count-controlled loops.

• Example Syntax: for num in range(5): print(num)

Example of for Loop: Display Numbers

Program 4-4 (simple_loop1.py)

• Displays numbers from 1 to 5.

Example of for Loop with a List

Program 4-7 (simple_loop3.py)

• Demonstrates looping over a list of strings.

Letting the User Control Loop Iterations

• Concept: Allow users to define the maximum loop iterations.

• Example: Program modified to accept user input for upper limit, retaining the same mechanics of the loop.

Augmented Assignment Operators

• Table 4-1 shows how various assignment operations can be simplified with augmented operators like +=, -=, *=, /=.

Nested Loops

• Definition: A loop within another loop.

• Analogy: A clock's hands functioning as nested loops, each performing different iterations.

• Example: Clock simulator with nested loops for seconds, minutes, and hours.

Example of Nested Loop: Average Test Scores

Program 4-17 (test_score_averages.py)

1. Collect number of students and test scores per student.

2. Loop through students and their respective scores to calculate average.

3. Output average for each student.