Dec 31, 2022

Lesson 3: Control structures in Python

 In this lesson, we will learn about control structures in Python and how to use them to control the flow of your program.

In Python, there are three main control structures that you can use: if statements, for loops, and while loops.

If statements

An if statement allows you to execute a block of code only if a certain condition is met.

Here is an example of how to use an if statement:

age = 30
if age >= 18:
    print('You are old enough to vote.')

In this example, the if statement checks if the value of the age variable is greater than or equal to 18. If it is, the code block within the if statement is executed and the message 'Youare old enough to vote.' is printed to the console. If the condition is not met, the code block is skipped.

You can also use the else keyword to specify a block of code that should be executed if the condition is not met.

Here is an example of how to use an if statement with an else clause:

age = 15
if age >= 18:
    print('You are old enough to vote.')
else:
    print('You are not old enough to vote.')

In this example, the if statement checks if the value of the age variable is greater than or equal to 18. If it is, the code block within the if statement is executed and the message 'You are old enough to vote.' is printed to the console. If the condition is not met, the code block within the else clause is executed and the message 'You are not old enough to vote.' is printed to the console.

You can also use the elif keyword (short for 'else if') to specify additional conditions that should be checked.

Here is an example of how to use an if statement with multiple elif clauses:

age = 15
if age >= 18:
    print('You are old enough to vote.')
elif age >= 16:
    print('You are old enough to drive.')
elif age >= 13:
    print('You are old enough to watch rated PG movies.')
else:
    print('You are not old enough to do any of the above.')

In this example, the if statement checks if the value of the age variable is greater than or equal to 18. If it is, the code block within the first if statement is executed and the message 'You are old enough to vote.' is printed to the console. If the condition is not met, the elif clauses are checked in order. If the condition of one of the elif clauses is met, the corresponding code block is executed and the appropriate message is printed to the console. If none of the conditions are met, the code block within the else clause is executed and the message 'You are not old enough to do any of the above.' is printed to the console.

For loops

A for loop allows you to execute a block of code multiple times, based on a sequence of items.

Here is an example of how to use a for loop:

fruits = ['apple', 'banana', 'orange', 'mango']
for fruit in fruits:
    print(fruit)

In this example, the for loop iterates over the list of fruits and prints each fruit to the console.

You can also use the range() function to create a sequence of numbers to iterate over.

Here is an example of how to use a for loop with the range() function:

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

This will print the numbers 0 through 4 to the console.You can also specify a start and end value for the range() function, as well as a step value.

Here is an example of how to use the range() function with start, end, and step values:

for i in range(2, 10, 2):

This will print the numbers 2, 4, 6, 8 to the console.

While loops

A while loop allows you to execute a block of code multiple times as long as a certain condition is met.

Here is an example of how to use a while loop:

i = 0
while i < 5:
    print(i)
    i += 1

In this example, the while loop will print the numbers 0 through 4 to the console. The i += 1 statement is used to increment the value of i by 1 after each iteration of the loop.

It's important to make sure that the condition of the while loop will eventually become False, otherwise the loop will run indefinitely and you will have an infinite loop.

Breaking out of loops

Sometimes, you may want to break out of a loop early if a certain condition is met. In Python, you can use the break statement to break out of a loop.

Here is an example of how to use the break statement:

for i in range(10):
    if i == 5:
        break
    print(i)

In this example, the for loop will iterate over the numbers 0 through 9. When the value of i is 5, the break statement is executed and the loop is terminated. This will print the numbers 0 through 4 to the console.

Continuing loop iterations

Sometimes, you may want to skip the rest of the current iteration of a loop and move on to the next one. In Python, you can use the continue statement to do this.

Here is an example of how to use the continue statement:

for i in range(10):
    if i % 2 == 1:  # if i is odd
        continue
    print(i)

In this example, the for loop will iterate over the numbers 0 through 9. If the value of i is odd, the continue statement is executed and the loop continues to the next iteration. This will print the numbers 0, 2, 4, 6, 8 to the console.

By