If statement execution flow in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does an if statement do in Python?

It checks a condition and runs a block of code only if that condition is true.

beginner

What happens if the if condition is false and there is no else block?

The program skips the if block and continues with the next code after it.

intermediate

How does an elif statement work in an if-elif-else chain?

It checks its condition only if all previous if and elif conditions were false.

beginner

What is the role of the else block in an if statement?

It runs a block of code when all previous if and elif conditions are false.

beginner

Consider this code:

if x > 10:
  print('Big')
elif x > 5:
  print('Medium')
else:
  print('Small')

What will print if x = 7?

It will print Medium because x > 10 is false but x > 5 is true.

What happens when the if condition is true?

A The code inside the <code>if</code> block runs.

B The code inside the <code>else</code> block runs.

C The program stops.

D The code inside the <code>elif</code> block runs.

When the if condition is true, only the code inside the if block runs.

If all if and elif conditions are false, which block runs?

A <code>if</code> block

B No block runs

C <code>elif</code> block

D <code>else</code> block

The else block runs when all previous conditions are false.

Can an if statement have multiple else blocks?

A Yes, as many as you want.

B No, only one <code>else</code> block is allowed.

C Only if you use <code>elif</code>.

D Only if the conditions are true.

An if statement can have only one else block.

What does the elif keyword mean?

A It ends the if statement.

B Else, it runs if all conditions are true.

C Else if, it checks another condition if previous ones are false.

D It repeats the if block.

elif means 'else if' and checks a new condition only if previous conditions were false.

What will this code print if score = 85?

if score >= 90:
  print('A')
elif score >= 80:
  print('B')
else:
  print('C')

A B

B A

C C

D Nothing

Since 85 is not >= 90 but is >= 80, it prints 'B'.

Explain how Python decides which block of code to run in an if-elif-else statement.

Think about the order Python checks conditions.

Describe what happens when an if condition is false and there is no else block.

What does the program do next?

Practice

1. What does an if statement do in Python?

easy

A. It stores data in a list.

B. It repeats code multiple times.

C. It runs code only if a condition is true.

D. It defines a new function.

Solution

1. Step 1: Understand the purpose of if

   An if statement checks a condition and runs code only if that condition is true.

2. Step 2: Compare with other options

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

3. Final Answer:

   It runs code only if a condition is true. -> Option C

4. Quick Check:

   if runs code if condition true [OK]

Hint: If checks condition; runs code only when true [OK]

Common Mistakes:

• Confusing if with loops
• Thinking if stores data
• Mixing if with function definition

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

easy

A. if x > 5 then:

B. if x > 5:

C. if (x > 5) {}

D. if x > 5 then

Solution

1. Step 1: Recall Python if syntax

   Python uses a colon : after the condition and no parentheses or 'then'.

2. Step 2: Check each option

   if x > 5: uses if x > 5: which is correct. Others use 'then' or braces which are not Python syntax.

3. Final Answer:

   if x > 5: -> Option B

4. Quick Check:

   Python if ends with colon [OK]

Hint: Python if ends with colon, no 'then' or braces [OK]

Common Mistakes:

• Adding 'then' after condition
• Using braces {} like other languages
• Forgetting the colon at the end

3. What will be the output of this code?

age = 20
if age < 18:
    print("Child")
elif age < 65:
    print("Adult")
else:
    print("Senior")

medium

A. Adult

B. Senior

C. Child

D. No output

Solution

1. Step 1: Check the value of age

   The variable age is 20.

2. Step 2: Evaluate conditions in order

   First condition age < 18 is false (20 is not less than 18). Second condition age < 65 is true (20 is less than 65), so it prints "Adult" and skips the else.

3. Final Answer:

   Adult -> Option A

4. Quick Check:

   20 is less than 65, prints Adult [OK]

Hint: Check conditions top to bottom; first true runs [OK]

Common Mistakes:

• Printing Child for age 20
• Ignoring elif and jumping to else
• Thinking no output if first condition false

4. Find the error in this code:

score = 75
if score >= 90
    print("Excellent")
elif score >= 60:
    print("Pass")
else:
    print("Fail")

medium

A. score variable not defined

B. Wrong indentation on print statements

C. Using elif instead of else if

D. Missing colon after first if condition

Solution

1. Step 1: Check syntax of if statement

   The first if line is missing a colon : at the end, which is required in Python.

2. Step 2: Verify other parts

   Indentation and elif usage are correct. The variable score is defined.

3. Final Answer:

   Missing colon after first if condition -> Option D

4. Quick Check:

   Every if needs a colon [OK]

Hint: Check colons after all if/elif/else lines [OK]

Common Mistakes:

• Forgetting colon after if condition
• Confusing elif with else if syntax
• Incorrect indentation of print lines

5. You want to print "Positive", "Zero", or "Negative" based on a number's value. Which code correctly uses if, elif, and else to do this?

hard

A. if num > 0:
print("Positive")
elif num == 0:
print("Zero")
else:
print("Negative")

B. if num > 0:
print("Positive")
if num == 0:
print("Zero")
else:
print("Negative")

C. if num > 0:
print("Positive")
else if num == 0:
print("Zero")
else:
print("Negative")

D. if num > 0:
print("Positive")
elif num < 0:
print("Zero")
else:
print("Negative")

Solution

1. Step 1: Understand correct if-elif-else structure

   Use if for first condition, elif for the second, and else for all other cases.

2. Step 2: Check each option

   if num > 0: print("Positive") elif num == 0: print("Zero") else: print("Negative") correctly uses elif and else. if num > 0: print("Positive") if num == 0: print("Zero") else: print("Negative") uses two separate if statements which can cause multiple prints. if num > 0: print("Positive") else if num == 0: print("Zero") else: print("Negative") uses invalid syntax else if. if num > 0: print("Positive") elif num < 0: print("Zero") else: print("Negative")'s elif num < 0 will print "Zero" for negative numbers and "Negative" for zero incorrectly.

3. Final Answer:

   if num > 0: print("Positive") elif num == 0: print("Zero") else: print("Negative") -> Option A

4. Quick Check:

   Use if, elif, else for exclusive conditions [OK]

Hint: Use if, elif, else for clear exclusive choices [OK]

Common Mistakes:

• Using multiple separate ifs causing multiple outputs
• Writing else if instead of elif
• Overlapping conditions causing wrong output