3 1 2 If-Else Statement Explained

Key Concepts

The 3 1 2 If-Else Statement in Python is a fundamental control flow structure used to make decisions in your code. The key concepts include:

• The if statement
• The else statement
• Combining if and else for decision-making

1. The if Statement

The if statement is used to execute a block of code only if a specified condition is true. If the condition is false, the code block is skipped.

Example:

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

Think of the if statement as a gatekeeper. If the condition is met, the gate opens, and the code inside the block is executed.

2. The else Statement

The else statement is used in conjunction with the if statement to execute a block of code when the if condition is false. It provides an alternative path for the program to follow.

Example:

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

Imagine the else statement as a backup plan. If the primary condition fails, the backup plan is executed.

3. Combining if and else for Decision-Making

By combining if and else statements, you can create decision-making structures that guide the flow of your program based on different conditions.

Example:

age = 18
if age >= 18:
    print("You are eligible to vote")
else:
    print("You are not eligible to vote")
    

In this example, the program checks the age and prints a message based on whether the person is eligible to vote or not.

Practical Examples

Let's look at some practical examples to see how if-else statements can be used in real-world scenarios.

Example: Checking Password Strength

password = "secure123"
if len(password) >= 8:
    print("Strong password")
else:
    print("Weak password")
    

In this example, the program checks the length of the password and determines its strength based on the length.

Example: Grading System

score = 75
if score >= 90:
    print("Grade: A")
elif score >= 80:
    print("Grade: B")
elif score >= 70:
    print("Grade: C")
else:
    print("Grade: D")
    

Here, the program assigns a grade based on the score, demonstrating how multiple conditions can be checked using elif (short for "else if").

Conclusion

The if-else statement is a powerful tool for controlling the flow of your Python programs. By understanding and effectively using if and else statements, you can create dynamic and responsive applications that make decisions based on different conditions.