If Condition

Why Do We Need Conditions?

The CPU (Central Processing Unit) is the brain of every computer. It consists of three major units:

The ALU has two sub-units:

• AU (Arithmetic Unit): Handles addition, subtraction, etc.

• LU (Logic Unit): Evaluates conditions like

  • Is the number even?
  • Is A > B?
  • Is the condition True or False?

The Logic Unit enables decision-making, and that is exactly what Python’s if statement uses.

The if Statement

The if statement allows Python to execute a block of code only when the condition is True.

Syntax

if condition:
    statements

Key Rules:

• Python does not use { } like C/C++.
• Code blocks are defined using indentation (4 spaces recommended).
• If the condition is False, the block is skipped.

Example:

if True:
    print("I'm right")

Output:

I'm right

Example (False condition):

if False:
    print("I'm right")
print("Bye")

Output:

Bye

Understanding Indentation in Python

Indentation is mandatory in Python and determines which statements belong to a block.

Example 1 (Both inside the block):

if True:
    print("Even")
    print("Bye")

Output:

Even
Bye

Example 2 (Only first line is inside the block):

if True:
    print("Even")
print("Bye")

Output:

Even
Bye

Example 3 (Condition False):

if False:
    print("Even")
print("Bye")

Output:

Bye

Making Decisions Using Conditions

Conditions evaluate to True or False, allowing programs to behave dynamically.

Example: Check if a number is even or odd.

num = int(input("Enter a number: "))

if num % 2 == 0:
    print("Even")

if num % 2 == 1:
    print("Odd")

print("Bye")

How it works:

• % is the modulus operator → gives remainder
• Even number → num % 2 == 0
• Odd number → num % 2 == 1

Usage of the if Statement

The if statement is used whenever a program must choose between different actions. Common uses include:

• Validating user input

  if age >= 18:
      print("Eligible to vote")

• Performing calculations based on conditions

  if marks >= 40:
      print("Pass")

• Executing code only when a condition is met

  if is_logged_in:
      show_dashboard()

• Checking for errors or special cases

  if filename == "":
      print("Filename cannot be empty")

• Making decisions in games, apps, and automation scripts

  if health <= 0:
      print("Game Over")

In short, any situation that requires decision-making uses if statements.

Summary

• The if statement is used to execute code only when a condition is True.
• Python determines code blocks using indentation, not curly braces.
• The Logic Unit (LU) of the CPU performs logical checks that help programs make decisions.
• Conditions like num % 2 == 0 return True/False, controlling program flow.
• Using if, Python can perform intelligent decisions such as checking even/odd, validating input, comparing values, etc.