Conditions with if and else

Conditional statements allow us to make decisions in our Python programs. The most common conditional is the if statement. With it, we can execute a block of code only if a certain condition is true.

The if Statement

The basic syntax of an if statement is:

if condition:
    # block of code

• If the condition is True, the code inside the block runs.
• If it's False, Python skips it.

Example:

age = 18
if age >= 18:
    print("You are an adult.")

Output

You are an adult.

Adding an else Clause

The else clause provides an alternative block of code to run if the condition is False.

Syntax:

if condition:
    # runs if condition is True
else:
    # runs if condition is False

Example:

age = 16
if age >= 18:
    print("You are an adult.")
else:
    print("You are underaged.")

Output

You are underaged.

Using Comparison Operators

Here are some operators you can use inside conditions:

Example:

score = 70
if score >= 50:
    print("You passed!")
else:
    print("You failed.")

Output

You passed!

Indentation is Mandatory

In Python, indentation matters. Blocks of code under if or else must be indented.

x = 5
if x > 0:
    print("Positive number")  # Correct indentation

Incorrect indentation will cause an error.

Nested Conditions

You can also nest if statements inside each other.

age = 20
if age > 0:
    if age >= 18:
        print("Adult")
    else:
        print("Child")

Exercise: Try It Yourself!

Write a program that asks the user for a number and prints:

• "Positive" if it's greater than 0
• "Zero" if it's equal to 0
• "Negative" if it's less than 0

Sample output

Enter a number: -3
Negative