Control Flow

Conditionals and Loops

Introduction

Control flow is the backbone of any programming language, allowing you to make decisions and repeat tasks based on specific conditions. In this post, we’ll explore Python’s conditionals (if, else, elif) and loops (for, while), along with key keywords like break and continue.

1. Conditionals: Making Decisions

Conditionals allow your program to execute specific blocks of code depending on the value of a condition (a Boolean expression).

Basic Syntax

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if condition:
    # Code to execute if condition is True
elif another_condition:
    # Code to execute if the first condition is False and this one is True
else:
    # Code to execute if all conditions are False

Examples

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age = 20

if age < 18:
    print("You are a minor.")
elif age >= 18 and age < 65:
    print("You are an adult.")
else:
    print("You are a senior.")

2. Logical Operators

Conditionals often use logical operators to combine or modify conditions:

  • and: True if both conditions are True.
  • or: True if at least one condition is True.
  • not: Reverses the condition.

Example:

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x = 10
y = 20

if x > 5 and y > 15:
    print("Both conditions are True.")

if not x < 5:
    print("x is not less than 5.")

3. Loops: Repeating Tasks

The for Loop

The for loop iterates over a sequence (like a list, string, or range).

Example 1: Iterating Over a List

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fruits = ["apple", "banana", "cherry"]

for fruit in fruits:
    print(fruit)

Example 2: Using range

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for i in range(5):  # 0 to 4
    print(i)

for i in range(1, 6):  # 1 to 5
    print(i)

The while Loop

The while loop continues executing as long as the condition is True.

Example:

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count = 0

while count < 5:
    print(count)
    count += 1  # Increment count

4. Controlling Loops

The break Statement

Exits the loop immediately.

Example:

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for i in range(10):
    if i == 5:
        break  # Exit the loop
    print(i)

The continue Statement

Skips the current iteration and moves to the next.

Example:

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for i in range(10):
    if i % 2 == 0:
        continue  # Skip even numbers
    print(i)

5. Nested Conditionals and Loops

You can nest conditionals inside loops and vice versa to handle more complex scenarios.

Example:

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for i in range(1, 6):
    if i % 2 == 0:
        print(f"{i} is even.")
    else:
        print(f"{i} is odd.")

6. Infinite Loops

Be cautious when writing loops. Forgetting to update the condition can lead to infinite loops.

Example of an Infinite Loop (Avoid This!)

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while True:
    print("This will run forever!")

To stop such a loop, you can press Ctrl+C in your terminal.

Conclusion

With conditionals and loops, you can control the flow of your Python programs effectively. These tools enable you to build flexible and powerful logic.