COMP121L_Repetition_Structure

Lesson Overview

• Lesson Title: Repetition Structure

• Instructor: HANNAH SHAMIRA P. SANTONIL

• Institution: Manuel S. Enverga University Foundation, College of Engineering

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 executes a statement or set of statements repeatedly.

• Purpose: To avoid writing the same code multiple times, making code cleaner and more efficient.

• Common term: Repetition structure is often referred to as a loop.

Types of Loops

Condition-Controlled Loops

• Definition: Uses a true/false condition to control repetitions.

• Implementation in Python: Usually written using the while statement.

Count-Controlled Loops

• Definition: Repeats a specific number of times.

• Implementation in Python: Written using the for statement.

The while Loop

Concept

• Condition-Controlled: Executes a statement or block of statements as long as a specified condition is true.

Parts of the While Loop

1. Condition: Evaluated for true/false value.

2. Statements: Executed repeatedly while the condition is true.

General Format in Python

while condition:
    statement
    statement

Example 1: Calculating Sales Commissions

keep_going = 'y'
while keep_going == 'y':
    sales = float(input('Enter the amount of sales: '))
    comm_rate = float(input('Enter the commission rate: '))
    commission = sales * comm_rate
    print('The commission is $', format(commission, ',.2f'), sep='')
    keep_going = input('Do you want to calculate another commission (Enter y for yes): ')

• Program Output: Calculates the commission based on user input.

Figure 4-2: Logic Flow of the While Loop

• If the condition is true, execute statements; if false, skip to exit.

Pretest Loop

• The while loop is classified as a pretest loop, as it checks the condition before executing the loop.

• Often requires initial steps to ensure execution at least once.

Example 2: Substance Heating Process

Algorithm

1. Get the substance's temperature.

2. Repeat the following steps while the temperature exceeds 102.5°C:

   • Adjust the thermostat and wait 5 minutes.

   • Check the temperature again.

3. After completion, advise technician to check temperature again in 15 minutes.

Example of Python code

MAX_TEMP = 102.5
temperature = float(input("Enter the substance's Celsius temperature: "))
while temperature > MAX_TEMP:
    print('Temperature too high. Adjust thermostat and wait 5 minutes.')
    temperature = float(input('Enter new temperature: '))
print('Temperature acceptable. Check in 15 minutes.')

The for Loop

Concept

• Count-Controlled Loop: Iterates a specific number of times.

• Syntax:

for variable in [value1, value2]:
    statement

Using the Range Function

• Purpose: Simplifies creating count-controlled loops by generating a sequence of numbers.

• Basic Usage:

for num in range(5):
    print(num)

• Details: Generates numbers from 0 to 4.

Example: Using Range Function

• With a single argument: Displays "Hello world" five times.

• With two arguments: Defines start and end of the range:

for num in range(1, 5):
    print(num)

• With three arguments: Defines a start, end, and step:

for num in range(1, 10, 2):
    print(num)

Using the Target Variable Inside the Loop

• Definition: The target variable represents each item in the sequence as the loop iterates.

• Example Task: Display numbers and their squares in a formatted table.

Nested Loops

Concept

• Definition: A loop inside another loop.

• Analogy: A clock with hands rotating at different rates.

Example: Digital Clock Simulation

• Displays seconds from 0-59, nests minute count into that.

Sample Code: Nested Loop Program

num_students = int(input('How many students? '))
for student in range(num_students):
    num_test_scores = int(input('How many test scores? '))
    for test_num in range(num_test_scores):
        score = float(input(': '))
        total += score
    average = total / num_test_scores
    print('Average for student', student+1, 'is:', average)

Conclusion

• Understanding repetition structures is crucial in programming for efficiency and functionality.