Ternary operator in C++ - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of nested ternary operator

What is the output of this C++ code snippet?

C++

int x = 5, y = 10;
int result = (x > y) ? (x - y) : ((x == y) ? 0 : (y - x));
std::cout << result << std::endl;

A 0

B -5

C 5

D 10

💡 Hint

Remember the ternary operator evaluates conditions from left to right.

Since x (5) is not greater than y (10), the first condition is false. Then it checks if x == y, which is false. So it returns y - x, which is 10 - 5 = 5.

❓ Predict Output

intermediate

Ternary operator with side effects

What will be printed by this C++ code?

C++

int a = 3, b = 4;
int c = (a > b) ? (a += 2) : (b += 3);
std::cout << a << " " << b << " " << c << std::endl;

A 3 7 7

B 5 4 5

C 5 7 7

D 3 4 3

💡 Hint

Check which condition is true and which variable is updated.

Since a (3) is not greater than b (4), the else part runs, so b is increased by 3 to 7, and c gets the value 7. a remains 3.

🧠 Conceptual

advanced

Understanding ternary operator associativity

Consider the expression: int x = 1 ? 0 : 1 ? 2 : 3; What is the value of x after this statement?

A 2

B 0

C 3

D 1

💡 Hint

Ternary operators associate from right to left.

The expression is parsed as int x = 1 ? 0 : (1 ? 2 : 3); Since 1 is true, x is assigned 0.

❓ Predict Output

advanced

Ternary operator with different types

What is the output of this code snippet?

C++

auto val = true ? 3.5 : 2;
std::cout << typeid(val).name() << " " << val << std::endl;

A d 3.5

B i 2

C f 3.5

D i 3

💡 Hint

Check the type deduced by the ternary operator when operands have different types.

The ternary operator promotes int 2 to double 2.0, so val is double (typeid name 'd') and value 3.5.

🔧 Debug

expert

Identify the error in ternary operator usage

Which option will cause a compilation error in this code snippet?

C++

int a = 5, b = 10;
int result = (a > b) ? a : "10";
std::cout << result << std::endl;

A int result = (a > b) ? a : static_cast<int>(10);

B int result = (a > b) ? a : (int)10;

C int result = (a > b) ? a : 10;

D int result = (a > b) ? a : "10";

💡 Hint

Check the types of the values returned by the ternary operator.

Option D uses a string literal "10" which cannot be assigned to int result, causing a compilation error.

Practice

1. What does the ternary operator condition ? value_if_true : value_if_false do in C++?

easy

A. It comments out a line of code.

B. It creates a loop that runs twice.

C. It declares a new variable.

D. It chooses one of two values based on the condition's truth.

Solution

1. Step 1: Understand the ternary operator syntax

   The ternary operator uses a condition followed by a question mark, then two values separated by a colon.

2. Step 2: Identify its purpose

   It returns the first value if the condition is true, otherwise the second value.

3. Final Answer:

   It chooses one of two values based on the condition's truth. -> Option D

4. Quick Check:

   condition ? true_value : false_value = chooses value [OK]

Hint: Remember: condition ? true : false picks one value [OK]

Common Mistakes:

• Thinking it creates loops
• Confusing it with variable declaration
• Assuming it comments code

2. Which of the following is the correct syntax for the ternary operator in C++?

easy

A. condition ? value_if_true : value_if_false;

B. condition : value_if_true ? value_if_false;

C. condition ? value_if_true, value_if_false;

D. condition ? (value_if_true : value_if_false);

Solution

1. Step 1: Recall the ternary operator syntax

   The correct syntax is: condition ? value_if_true : value_if_false;

2. Step 2: Check each option

   condition ? value_if_true : value_if_false; matches the correct syntax exactly; others have misplaced symbols or punctuation.

3. Final Answer:

   condition ? value_if_true : value_if_false; -> Option A

4. Quick Check:

   Syntax = condition ? true : false; [OK]

Hint: Remember: question mark before colon in ternary [OK]

Common Mistakes:

• Swapping question mark and colon
• Using comma instead of colon
• Adding extra parentheses incorrectly

3. What is the output of this C++ code?

int x = 10, y = 20;
int max = (x > y) ? x : y;
std::cout << max;

medium

A. true

B. 10

C. 20

D. Syntax error

Solution

1. Step 1: Evaluate the condition (x > y)

   Since x is 10 and y is 20, (10 > 20) is false.

2. Step 2: Apply the ternary operator

   Because the condition is false, the value after the colon (y) is chosen, which is 20.

3. Final Answer:

   20 -> Option C

4. Quick Check:

   (10 > 20) ? 10 : 20 = 20 [OK]

Hint: Check condition result true or false to pick value [OK]

Common Mistakes:

• Choosing the first value always
• Confusing > with <
• Expecting boolean output

4. Find the error in this C++ code using the ternary operator:

int a = 5, b = 8;
int result = a > b ? a, b;
std::cout << result;

medium

A. Variables a and b are not initialized

B. Incorrect use of comma instead of colon in ternary operator

C. Missing semicolon after variable declaration

D. Ternary operator cannot be used with integers

Solution

1. Step 1: Identify the ternary operator syntax error

   The code uses a comma instead of a colon between the two values after the condition.

2. Step 2: Understand the correct syntax

   The ternary operator requires a colon to separate true and false values: condition ? true_value : false_value.

3. Final Answer:

   Incorrect use of comma instead of colon in ternary operator -> Option B

4. Quick Check:

   Use ':' not ',' in ternary [OK]

Hint: Use ':' to separate values in ternary, not ',' [OK]

Common Mistakes:

• Using comma instead of colon
• Forgetting to separate values properly
• Assuming ternary works like comma operator

5. Given this code, what will be the value of result?

int x = 0;
int y = 5;
int result = (x != 0) ? (y / x) : y * 2;
std::cout << result;

Note: Division by zero causes runtime error.

hard

A. 10

B. Runtime error (division by zero)

C. 0

D. 5

Solution

1. Step 1: Evaluate the condition (x != 0)

   Since x is 0, (0 != 0) is false.

2. Step 2: Apply the ternary operator safely

   Because the condition is false, the expression after the colon is chosen: y * 2 = 5 * 2 = 10.

3. Final Answer:

   10 -> Option A

4. Quick Check:

   Condition false, so result = y*2 = 10 [OK]

Hint: Check condition first to avoid division by zero [OK]

Common Mistakes:

• Assuming division runs even if condition false
• Ignoring division by zero risk
• Choosing wrong expression side