If–else statement in C++ - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if a number is positive.

C++

int num = 5;
if (num [1] 0) {
    std::cout << "Positive" << std::endl;
}

Drag options to blanks, or click blank then click option'

A>

B==

C<

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' instead of '>' to check positivity.

Using '<' which checks for negative numbers.

The condition num > 0 checks if the number is positive.

2fill in blank

medium

Complete the code to print "Even" if the number is even.

C++

int num = 4;
if (num % 2 [1] 0) {
    std::cout << "Even" << std::endl;
}

Drag options to blanks, or click blank then click option'

A<

B!=

C>

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' which checks for odd numbers.

Using '>' or '<' which are not suitable here.

The condition num % 2 == 0 checks if the number is even.

3fill in blank

hard

Fix the error in the if–else statement to print "Positive" or "Non-positive".

C++

int num = -3;
if (num [1] 0) {
    std::cout << "Positive" << std::endl;
} else {
    std::cout << "Non-positive" << std::endl;
}

Drag options to blanks, or click blank then click option'

A==

B<=

C>

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<=' which reverses the logic.

Using '==' which only checks for zero.

The condition num > 0 correctly checks for positive numbers.

4fill in blank

hard

Fill both blanks to print "Adult" if age is 18 or more, otherwise "Minor".

C++

int age = 20;
if (age [1] 18) {
    std::cout << "Adult" << std::endl;
} else {
    std::cout << "[2]" << std::endl;
}

Drag options to blanks, or click blank then click option'

A>=

B<

CMinor

DAdult

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>=' for the condition.

Printing "Adult" in the else block.

The condition age >= 18 checks if the person is an adult. Otherwise, print "Minor".

5fill in blank

hard

Fill all three blanks to print "Positive", "Negative", or "Zero" based on the value of num.

C++

int num = 0;
if (num [1] 0) {
    std::cout << "Positive" << std::endl;
} else if (num [2] 0) {
    std::cout << "Negative" << std::endl;
} else {
    std::cout << "[3]" << std::endl;
}

Drag options to blanks, or click blank then click option'

A>

B<

CZero

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' which does not distinguish zero.

Mixing up the comparison operators.

The first condition checks if num > 0 (positive), the second if num < 0 (negative), else print "Zero".

Practice

1. What does an if-else statement do in C++?

easy

A. It defines a function.

B. It repeats a block of code multiple times.

C. It chooses between two paths based on a condition.

D. It declares a variable.

Solution

1. Step 1: Understand the purpose of if-else

   An if-else statement lets the program decide which block of code to run based on a condition.

2. Step 2: Compare with other options

   Repeating code is done by loops, functions define reusable code, and variables store data, so these are not correct.

3. Final Answer:

   It chooses between two paths based on a condition. -> Option C

4. Quick Check:

   If-else = choose path [OK]

Hint: If condition true, run if-block; else run else-block [OK]

Common Mistakes:

• Confusing if-else with loops
• Thinking if-else defines functions
• Mixing variable declaration with control flow

2. Which of the following is the correct syntax for an if-else statement in C++?

easy

A. if (x > 0) { cout << "Positive"; } else { cout << "Non-positive"; }

B. if x > 0 then cout << "Positive" else cout << "Non-positive"

C. if (x > 0) cout << "Positive" else cout << "Non-positive";

D. if x > 0 { cout << "Positive" } else { cout << "Non-positive" }

Solution

1. Step 1: Check C++ if-else syntax rules

   C++ requires parentheses around the condition and braces around blocks for multiple statements.

2. Step 2: Analyze each option

   if (x > 0) { cout << "Positive"; } else { cout << "Non-positive"; } uses correct parentheses and braces. Options A and B miss parentheses or use incorrect keywords. if (x > 0) cout << "Positive" else cout << "Non-positive"; misses semicolon after else block.

3. Final Answer:

   if (x > 0) { cout << "Positive"; } else { cout << "Non-positive"; } -> Option A

4. Quick Check:

   Correct syntax uses parentheses and braces [OK]

Hint: Use parentheses for condition and braces for blocks [OK]

Common Mistakes:

• Omitting parentheses around condition
• Missing braces for multiple statements
• Using 'then' keyword (not in C++)

3. What will be the output of this code?

int x = 5;
if (x < 3) {
  cout << "Less";
} else {
  cout << "More or equal";
}

medium

A. Less

B. More or equal

C. No output

D. Compilation error

Solution

1. Step 1: Evaluate the condition x < 3

   Variable x is 5, so 5 < 3 is false.

2. Step 2: Determine which block runs

   Since condition is false, the else block runs, printing "More or equal".

3. Final Answer:

   More or equal -> Option B

4. Quick Check:

   Condition false -> else block output [OK]

Hint: Check condition truth to pick if or else output [OK]

Common Mistakes:

• Assuming if-block runs when condition is false
• Confusing output strings
• Ignoring else block

4. Find the error in this code snippet:

int n = 10;
if n > 5 {
  cout << "Big";
} else {
  cout << "Small";
}

medium

A. Missing parentheses around condition

B. Missing semicolon after cout statements

C. Incorrect else keyword

D. Variable n not declared

Solution

1. Step 1: Check if statement syntax

   C++ requires parentheses around the condition in if statements.

2. Step 2: Identify the error

   The code uses if n > 5 without parentheses, which is invalid syntax.

3. Final Answer:

   Missing parentheses around condition -> Option A

4. Quick Check:

   if condition needs parentheses [OK]

Hint: Always put condition inside parentheses in if [OK]

Common Mistakes:

• Omitting parentheses in if condition
• Forgetting semicolons (though not the main error here)
• Misreading else keyword

5. You want to write a program that prints "Even" if a number is divisible by 2, otherwise prints "Odd". Which code correctly uses if-else to do this?

hard

A. if (num % 2 = 0) { cout << "Even"; } else { cout << "Odd"; }

B. if (num / 2 == 0) { cout << "Even"; } else { cout << "Odd"; }

C. if (num % 2 != 0) { cout << "Even"; } else { cout << "Odd"; }

D. if (num % 2 == 0) { cout << "Even"; } else { cout << "Odd"; }

Solution

1. Step 1: Understand divisibility by 2

   A number is divisible by 2 if remainder when divided by 2 is zero, i.e., num % 2 == 0.

2. Step 2: Check each option's condition

   if (num % 2 == 0) { cout << "Even"; } else { cout << "Odd"; } correctly uses num % 2 == 0. if (num / 2 == 0) { cout << "Even"; } else { cout << "Odd"; } uses division instead of modulo. if (num % 2 = 0) { cout << "Even"; } else { cout << "Odd"; } uses assignment (=) instead of comparison (==). if (num % 2 != 0) { cout << "Even"; } else { cout << "Odd"; } reverses the logic.

3. Final Answer:

   if (num % 2 == 0) { cout << "Even"; } else { cout << "Odd"; } -> Option D

4. Quick Check:

   Use modulo == 0 for even check [OK]

Hint: Use modulo (%) and == 0 to check even numbers [OK]

Common Mistakes:

• Using assignment (=) instead of comparison (==)
• Using division (/) instead of modulo (%)
• Reversing if and else blocks