B1. Python if...else Statement

In Python, the if...else statement is a conditional statement that allows you to execute different code blocks based on whether a certain condition is true or false. The basic syntax of an if...else statement is as follows:

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

Here, condition is a boolean expression that evaluates to either True or False. If the condition is true, the code block inside the if statement is executed, and if the condition is false, the code block inside the else statement is executed.

You can also use elif (short for “else if”) statements to chain multiple conditions together, like this:

if condition1:
    # code to execute if condition1 is true
elif condition2:
    # code to execute if condition2 is true and condition1 is false
else:
    # code to execute if both condition1 and condition2 are false

In this case, if condition1 is true, the code block inside the first if statement is executed, and the rest of the elif and else statements are skipped. If condition1 is false, then condition2 is checked.

If condition2 is true, the code block inside the second elif statement is executed, and if both condition1 and condition2 are false, the code block inside the else statement is executed.

Example for Python if..else : #

Beow is an example of how to use the if...else statement in Python:

# Check if a number is even or odd
num = 4

if num % 2 == 0:
    print("The number is even.")
else:
    print("The number is odd.")

In this example, we’re checking if the value of num is even or odd. We use the modulo operator (%) to check if num is divisible by 2 with no remainder.

If the remainder is 0, then num is even and the code block inside the if statement is executed, which prints “The number is even.” If the remainder is not 0, then num is odd and the code block inside the else statement is executed, which prints “The number is odd.” In this case, since num is 4, which is even, the output will be “The number is even.”

Python if..elif..else explained : #

The if...elif...else statement in Python allows you to evaluate multiple conditions and execute different blocks of code based on the result of those conditions. It’s similar to the if...else statement, but allows you to test additional conditions if the first condition is false.

The basic syntax of an if...elif...else statement is as follows:

if condition1:
    # code to execute if condition1 is true
elif condition2:
    # code to execute if condition2 is true and condition1 is false
elif condition3:
    # code to execute if condition3 is true and both condition1 and condition2 are false
else:
    # code to execute if all conditions are false

Here, condition1, condition2, and condition3 are boolean expressions that evaluate to either True or False. If condition1 is true, the code block inside the first if statement is executed, and the rest of the elif and else statements are skipped. If condition1 is false, then condition2 is checked. If condition2 is true, the code block inside the second elif statement is executed, and so on.

If none of the conditions are true, the code block inside the else statement is executed.

Example for Python if…elif…else : #

Here’s an example of how to use the if...elif...else statement in Python:

# Check if a number is positive, negative, or zero
num = -4

if num > 0:
    print("The number is positive.")
elif num == 0:
    print("The number is zero.")
else:
    print("The number is negative.")

In this example, we’re checking if the value of num is positive, negative, or zero. We use if to check if num is greater than 0, and if it is, we print “The number is positive.”

If num is not greater than 0, we move on to the elif statement, where we check if num is equal to 0, and if it is, we print “The number is zero.” If num is not greater than 0 and not equal to 0, we move on to the else statement, where we print “The number is negative.” In this case, since num is -4, the output will be “The number is negative.”

Nested if..else in Python : #

In Python, a nested if statement is an if statement that is inside another if statement. This is useful when you need to test multiple conditions and execute different blocks of code based on the result of those conditions.

The basic syntax of a nested if statement is as follows:

if condition1:
    # code to execute if condition1 is true
    if condition2:
        # code to execute if condition1 and condition2 are true
    else:
        # code to execute if condition1 is true and condition2 is false
else:
    # code to execute if condition1 is false

Here, condition1 and condition2 are boolean expressions that evaluate to either True or False. If condition1 is true, the code block inside the first if statement is executed, and then the code inside the nested if statement is executed if condition2 is also true. If condition1 is true but condition2 is false, the code block inside the else statement is executed.

If condition1 is false, the code block inside the else statement is executed.

Example for Nested if..else in python : #

Here’s an example of how to use a nested if statement in Python:

# Check if a number is positive, negative, or zero and even or odd
num = -4

if num >= 0:
    if num % 2 == 0:
        print("The number is positive and even.")
    else:
        print("The number is positive and odd.")
else:
    if num % 2 == 0:
        print("The number is negative and even.")
    else:
        print("The number is negative and odd.")

In this example, we’re checking if the value of num is positive, negative, or zero, and whether it’s even or odd. We use a nested if statement to check if num is greater than or equal to 0.

If it is, we check if num is even or odd using the modulo operator (%). If num is even, we print “The number is positive and even.” If num is odd, we print “The number is positive and odd.”

If num is not greater than or equal to 0, we move on to the else statement. If num is even, we print “The number is negative and even.” If num is odd, we print “The number is negative and odd.” In this case, since num is -4, which is negative and even, the output will be “The number is negative and even.”