Introduction to if...else Statements

 In Python, conditional statements allow us to execute certain code based on specific conditions. The if...else statement is one of the most commonly used control flow statements that helps in decision-making. It executes a block of code if a specified condition is true. Otherwise, it executes an alternative block of code.

Syntax

if condition:
    # code to execute if condition is true
else:
    # code to execute if condition is false

Basic Usage

Simple if Statement

A simple if statement checks a condition and executes the indented block of code only if the condition is true.

if...else Statement

An if...else statement allows us to define an alternative block of code that runs if the condition is false.

Example Codes

Example 1: Basic if Statement

x = 10
if x > 5:
    print("x is greater than 5")

Example 2: if...else Statement

x = 3
if x > 5:
    print("x is greater than 5")
else:
    print("x is not greater than 5")

Example 3: Nested if Statements

x = 15
if x > 10:
    print("x is greater than 10")
    if x > 20:
        print("x is also greater than 20")
    else:
        print("x is not greater than 20")

Example 4: if...elif...else Ladder

x = 7
if x > 10:
    print("x is greater than 10")
elif x == 10:
    print("x is 10")
else:
    print("x is less than 10")

Example 5: Checking for Even or Odd Number

num = 4
if num % 2 == 0:
    print(f"{num} is an even number")
else:
    print(f"{num} is an odd number")

Example 6: Checking for Positive, Negative, or Zero

num = 0
if num > 0:
    print(f"{num} is a positive number")
elif num < 0:
    print(f"{num} is a negative number")
else:
    print("The number is zero")

Example 7: Finding the Largest Number Among Three

a = 5
b = 8
c = 3
if a >= b and a >= c:
    print(f"{a} is the largest number")
elif b >= a and b >= c:
    print(f"{b} is the largest number")
else:
    print(f"{c} is the largest number")

Example 8: Checking Leap Year

year = 2024
if (year % 4 == 0 and year % 100 != 0) or (year % 400 == 0):
    print(f"{year} is a leap year")
else:
    print(f"{year} is not a leap year")

Example 9: Grading System

score = 85
if score >= 90:
    grade = 'A'
elif score >= 80:
    grade = 'B'
elif score >= 70:
    grade = 'C'
elif score >= 60:
    grade = 'D'
else:
    grade = 'F'
print(f"Grade: {grade}")

Example 10: Password Validation

python
password = "secret123"
if len(password) < 6:
    print("Password is too short")
elif len(password) > 12:
    print("Password is too long")
else:
    print("Password is valid")

Conclusion

The if...else statement is a fundamental concept in Python programming that helps in making decisions based on conditions. By understanding and practicing with these examples, you'll be well-equipped to handle conditional logic in your Python programs. Keep experimenting with different conditions and scenarios to deepen your understanding. Happy coding!