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

Condition: Evaluated for true/false value.
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

Get the substance's temperature.
Repeat the following steps while the temperature exceeds 102.5°C:
- Adjust the thermostat and wait 5 minutes.
- Check the temperature again.
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.