Why conditional logic is needed in C++ - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print "Adult" if age is 18 or more.

C++

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

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

A>=

B<

C==

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' will check if age is less than 18, which is wrong here.

Using '==' checks only if age is exactly 18, not more.

The condition age >= 18 checks if age is 18 or more, so it prints "Adult" correctly.

2fill in blank

medium

Complete the code to print "Even" if the number is divisible by 2.

C++

int number = 10;
if (number [1] 2 == 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 '/' divides the number but does not check for evenness.

Using '*' or '+' does not relate to divisibility.

The modulus operator % gives the remainder. If number % 2 == 0, the number is even.

3fill in blank

hard

Fix the error in the condition to check if score is less than 50.

C++

int score = 45;
if (score [1] 50) {
    std::cout << "Fail" << std::endl;
}

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

A>

B==

C>=

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>' checks if score is greater than 50, which is wrong here.

Using '>=' or '==' do not check for less than.

The condition score < 50 correctly checks if the score is less than 50 to print "Fail".

4fill in blank

hard

Fill both blanks to print "Teenager" if age is between 13 and 19 inclusive.

C++

int age = 15;
if (age [1] 13 && age [2] 19) {
    std::cout << "Teenager" << std::endl;
}

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

A>=

B<

C<=

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' or '>' alone excludes boundary ages.

Using wrong operators reverses the logic.

The condition age >= 13 && age <= 19 checks if age is between 13 and 19 inclusive.

5fill in blank

hard

Fill in the blanks to print "Grade A" if score is above 90, "Grade B" if score is above 80, else "Grade C".

C++

int score = 85;
if (score [1] 90) {
    std::cout << "Grade A" << std::endl;
} else if (score [2] 80) {
    std::cout << "Grade B" << std::endl;
} else {
    std::cout << "Grade C" << std::endl;
}

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

A>

B>=

C<=

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>=' includes the boundary which may change grading logic.

Using '<=' or '<' in conditions here is incorrect.

The conditions use score > 90 and score > 80 to check if score is above 90 or 80, printing the appropriate grade.

Practice

1. Why do we use conditional logic like if statements in C++ programs?

easy

A. To store multiple values in a list

B. To repeat the same code many times

C. To make decisions and run different code based on conditions

D. To define new data types

Solution

1. Step 1: Understand the purpose of conditional logic

   Conditional logic allows a program to choose between different actions depending on whether a condition is true or false.

2. Step 2: Compare with other options

   Repeating code is done with loops, storing values uses arrays or vectors, and defining data types uses classes or structs, not conditional logic.

3. Final Answer:

   To make decisions and run different code based on conditions -> Option C

4. Quick Check:

   Conditional logic = decision making [OK]

Hint: Conditional logic = choosing what to do next [OK]

Common Mistakes:

• Confusing conditional logic with loops
• Thinking conditional logic stores data
• Mixing conditional logic with data type definitions

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

easy

A. if condition { /* code */ }

B. if (condition) { /* code */ }

C. if condition then { /* code */ }

D. if: (condition) { /* code */ }

Solution

1. Step 1: Recall C++ if statement syntax

   In C++, the condition must be inside parentheses and the code block inside curly braces: if (condition) { /* code */ }

2. Step 2: Check each option

   if condition { /* code */ } misses parentheses, C uses 'then' which is not C++ syntax, D uses a colon which is invalid.

3. Final Answer:

   if (condition) { /* code */ } -> Option B

4. Quick Check:

   Correct if syntax = if (condition) { } [OK]

Hint: If condition always in parentheses in C++ [OK]

Common Mistakes:

• Omitting parentheses around condition
• Using 'then' keyword incorrectly
• Adding colons after if

3. What will be the output of this C++ code?

int x = 10;
if (x > 5) {
  std::cout << "Big";
} else {
  std::cout << "Small";
}

medium

A. Small

B. 10

C. No output

D. Big

Solution

1. Step 1: Evaluate the condition x > 5

   Since x is 10, and 10 > 5 is true, the if block runs.

2. Step 2: Determine which output is printed

   The code prints "Big" because the if condition is true, so the else block is skipped.

3. Final Answer:

   Big -> Option D

4. Quick Check:

   10 > 5 is true, prints "Big" [OK]

Hint: Check if condition true or false to pick output [OK]

Common Mistakes:

• Confusing which block runs when condition is true
• Expecting variable value printed instead of string
• Ignoring else block

4. Find the error in this C++ code snippet:

int num = 7;
if num > 5 {
  std::cout << "Yes";
} else {
  std::cout << "No";
}

medium

A. Missing parentheses around condition in if statement

B. Missing semicolon after if statement

C. Incorrect use of else keyword

D. Variable num is not declared

Solution

1. Step 1: Check if statement syntax

   The condition in an if statement must be inside parentheses in C++. Here, it's missing.

2. Step 2: Verify other parts

   Semicolon after if is not needed, else keyword is correct, and num is declared properly.

3. Final Answer:

   Missing parentheses around condition in if statement -> Option A

4. Quick Check:

   If condition needs parentheses [OK]

Hint: If condition always inside ( ) in C++ [OK]

Common Mistakes:

• Forgetting parentheses around condition
• Adding unnecessary semicolon after if
• Misunderstanding else syntax

5. You want to write a program that prints "Adult" if age is 18 or more, and "Minor" otherwise. Which code correctly uses conditional logic to do this?

hard

A. if (age >= 18) { std::cout << "Adult"; } else { std::cout << "Minor"; }

B. if age >= 18 then std::cout << "Adult"; else std::cout << "Minor";

C. if (age > 18) std::cout << "Adult"; else std::cout << "Minor";

D. if (age = 18) { std::cout << "Adult"; } else { std::cout << "Minor"; }

Solution

1. Step 1: Check condition correctness

   The condition should be age >= 18 to include 18 as adult. if (age >= 18) { std::cout << "Adult"; } else { std::cout << "Minor"; } uses this correctly.

2. Step 2: Verify syntax and logic

   if age >= 18 then std::cout << "Adult"; else std::cout << "Minor"; uses 'then' which is invalid in C++. if (age > 18) std::cout << "Adult"; else std::cout << "Minor"; uses > 18, excluding 18 itself. if (age = 18) { std::cout << "Adult"; } else std::cout << "Minor"; } uses assignment (=) instead of comparison (==).

3. Final Answer:

   if (age >= 18) { std::cout << "Adult"; } else { std::cout << "Minor"; } -> Option A

4. Quick Check:

   Use >= and correct syntax for if-else [OK]

Hint: Use >= for 18 or more, and proper if-else syntax [OK]

Common Mistakes:

• Using assignment (=) instead of comparison (==)
• Using > instead of >= to include 18
• Adding 'then' keyword incorrectly