NCERT Computer Science Class #11 – Chapter #6 Solutions – Q #1

Chapter 6 – Flow of Control

Q #1 – What is the difference between else and elif construct of if statement?

The difference between the else and elif constructs in Python’s if statement lies primarily in their functionality and use cases.

‘else’ Statement

• Purpose: The else statement is used to define a block of code that will execute if the condition in the associated if statement evaluates to false.
• Usage: It provides a single alternative when there are only two possibilities (the condition being true or false).
• Syntax:

if condition:

    # Execute this block if condition is true

else:

    # Execute this block if condition is false

Example:

number = -1

if number > 0:

    print("The number is positive.")

else:

    print("The number is not positive.")

‘elif‘ Statement

• Purpose: The elif (short for “else if”) statement allows you to check multiple conditions sequentially. It provides additional conditions to check if the initial if condition is false.
• Usage: It is used when you have more than two alternatives to evaluate. You can have multiple elif statements following an if.
• Syntax:

if condition1:
    # Execute this block if condition1 is true
elif condition2:
    # Execute this block if condition2 is true
else:
    # Execute this block if all previous conditions are false

Example

marks = 85
if marks > 90:
    print("Grade: A+")
elif marks > 80:
    print("Grade: A")
elif marks > 70:
    print("Grade: B+")
else:
    print("Grade: C")

Key Differences

1. Number of Conditions:
   • Use else when you have only two possible outcomes (true or false).
   • Use elif when you need to evaluate multiple conditions.
2. Execution Flow:
   • The code in an else block executes only when the preceding if condition is false.
   • The code in an elif block executes only if its preceding conditions (if or other elif) are false.
3. Mutually Exclusive vs. Non-Mutually Exclusive:
   • An if-else structure implies mutually exclusive choices (only one can be true).
   • An if-elif-else structure allows for non-mutually exclusive choices, where only one block will execute based on the first true condition encountered.

By understanding these differences, you can effectively control the flow of your Python programs based on various conditions.

NCERT Computer Science Chapter 6 Solutions Q 1