Why conditional statements are needed in Python

Introduction

Conditional statements help a program make choices. They let the program do different things based on different situations.

When you want to check if a number is positive or negative and act differently.

When you want to decide if a user can log in based on their password.

When you want to give a discount only if the customer buys more than 5 items.

When you want to show a message only if it is raining.

When you want to stop a game if the player loses all lives.

Syntax

Python

if condition:
    # do something
elif another_condition:
    # do something else
else:
    # do something if no conditions above are true

Use if to check the first condition.

Use elif for additional conditions.

else runs if no conditions are true.

Examples

This checks if the temperature is above 30 and prints a message.

Python

if temperature > 30:
    print("It's hot outside!")

This chooses between two messages based on age.

Python

if age >= 18:
    print("You can vote.")
else:
    print("You are too young to vote.")

This uses multiple conditions to decide the grade.

Python

if score >= 90:
    print("Grade A")
elif score >= 80:
    print("Grade B")
else:
    print("Grade C or below")

Sample Program

This program checks the temperature and prints a message based on its value.

Python

temperature = 25
if temperature > 30:
    print("It's hot outside!")
elif temperature > 20:
    print("The weather is nice.")
else:
    print("It's a bit cold.")

Important Notes

Indentation is important in Python to show which code belongs to each condition.

Conditions must be something that can be true or false.

Summary

Conditional statements let programs make decisions.

They help run different code depending on the situation.

Use if, elif, and else to handle choices.

Practice

1. Why do we use conditional statements like if in Python?

easy

A. To repeat code multiple times

B. To store multiple values in a list

C. To make decisions and run code only when certain conditions are true

D. To define a function

Solution

1. Step 1: Understand the purpose of conditional statements

   Conditional statements check if something is true or false to decide what code to run.

2. Step 2: Compare with other options

   Repeating code is done by loops, storing values is done by lists, and defining functions uses def.

3. Final Answer:

   To make decisions and run code only when certain conditions are true -> Option C

4. Quick Check:

   Conditional statements = decision making [OK]

Hint: Think: 'Should I run this code or not?' [OK]

Common Mistakes:

• Confusing conditionals with loops
• Thinking conditionals store data
• Mixing conditionals with function definitions

2. Which of the following is the correct syntax for a simple if statement in Python?

easy

A. if x > 5: print('Yes')

B. if x > 5 print('Yes')

C. if (x > 5) { print('Yes') }

D. if x > 5 then print('Yes')

Solution

1. Step 1: Recall Python if syntax

   Python uses a colon (:) after the condition and indentation for the code block.

2. Step 2: Check each option

   if x > 5: print('Yes') uses colon and correct syntax; others use wrong keywords or braces not used in Python.

3. Final Answer:

   if x > 5: print('Yes') -> Option A

4. Quick Check:

   Colon and indentation = correct if syntax [OK]

Hint: Remember: Python uses ':' after condition [OK]

Common Mistakes:

• Using 'then' keyword (not in Python)
• Using braces {} like other languages
• Omitting colon after condition

3. What will be the output of this code?

age = 18
if age >= 18:
    print('Adult')
else:
    print('Child')

medium

A. Adult

B. No output

C. Child

D. Error

Solution

1. Step 1: Check the condition age >= 18

   Since age is 18, the condition is true.

2. Step 2: Determine which block runs

   The if block runs and prints 'Adult'. The else block is skipped.

3. Final Answer:

   Adult -> Option A

4. Quick Check:

   Condition true = 'Adult' printed [OK]

Hint: Check if condition is true or false [OK]

Common Mistakes:

• Assuming else block runs when condition is true
• Confusing >= with >
• Thinking no output if condition is true

4. Find the error in this code:

number = 10
if number > 5
    print('Big number')

medium

A. Indentation error in print statement

B. Missing colon ':' after the if condition

C. Wrong comparison operator

D. Variable 'number' is not defined

Solution

1. Step 1: Check the if statement syntax

   Python requires a colon ':' at the end of the if condition line.

2. Step 2: Identify the missing colon

   The code misses ':' after if number > 5, causing a syntax error.

3. Final Answer:

   Missing colon ':' after the if condition -> Option B

4. Quick Check:

   Colon missing after if condition [OK]

Hint: Always put ':' after if condition [OK]

Common Mistakes:

• Forgetting colon after if
• Misaligning indentation
• Changing comparison operator unnecessarily

5. You want to print 'Good morning' if the hour is less than 12, 'Good afternoon' if hour is between 12 and 18 (inclusive), and 'Good evening' otherwise. Which code correctly uses conditional statements?

hard

A. if hour < 12:
print('Good morning')
elif hour > 12 and hour < 18:
print('Good afternoon')
else:
print('Good evening')

B. if hour < 12:
print('Good morning')
if 12 <= hour <= 18:
print('Good afternoon')
else:
print('Good evening')

C. if hour < 12:
print('Good morning')
else if 12 <= hour <= 18:
print('Good afternoon')
else:
print('Good evening')

D. if hour < 12:
print('Good morning')
elif 12 <= hour <= 18:
print('Good afternoon')
else:
print('Good evening')

Solution

1. Step 1: Check correct use of if, elif, and else

   if hour < 12: print('Good morning') elif 12 <= hour <= 18: print('Good afternoon') else: print('Good evening') uses elif correctly and covers all hour ranges without overlap.

2. Step 2: Identify errors in other options

   if hour < 12: print('Good morning') if 12 <= hour <= 18: print('Good afternoon') else: print('Good evening') uses two separate if statements causing multiple prints; if hour < 12: print('Good morning') else if 12 <= hour <= 18: print('Good afternoon') else: print('Good evening') uses invalid 'else if' syntax; if hour < 12: print('Good morning') elif hour > 12 and hour < 18: print('Good afternoon') else: print('Good evening') misses equality for 12 and 18 in afternoon range.

3. Final Answer:

   Code with proper if, elif, and else and correct ranges -> Option D

4. Quick Check:

   Use elif for multiple conditions [OK]

Hint: Use elif for multiple exclusive conditions [OK]

Common Mistakes:

• Using 'else if' instead of 'elif'
• Using multiple separate if causing multiple outputs
• Incorrect range checks missing equal signs