Ternary operator in C++ - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the ternary operator in C++?

The ternary operator is a shorthand way to write an if-else statement. It uses the syntax: condition ? expression_if_true : expression_if_false;

beginner

How does the ternary operator work?

It evaluates the condition first. If the condition is true, it returns the first expression; if false, it returns the second expression.

beginner

Rewrite this if-else using the ternary operator:

if (a > b) {
  max = a;
} else {
  max = b;
}

max = (a > b) ? a : b;

intermediate

Can the ternary operator be nested in C++?

Yes, you can nest ternary operators inside each other, but it can make the code harder to read.

beginner

What is a common use case for the ternary operator?

It is often used for simple conditional assignments or returning values based on a condition in a single line.

What does the ternary operator syntax look like in C++?

A condition ? expr1 : expr2

B if (condition) expr1 else expr2

C condition ? expr1, expr2

D expr1 ? condition : expr2

The ternary operator uses the syntax: condition ? expression_if_true : expression_if_false.

What value does the ternary operator return if the condition is false?

A The second expression

B It returns nothing

C The condition itself

D The first expression

If the condition is false, the ternary operator returns the second expression.

Which of these is a valid use of the ternary operator?

A int x = if (a > b) a else b;

B int x = (a > b) ? a : b;

C int x = a > b ?;

D int x = a ? b :;

Option B correctly uses the ternary operator to assign the greater of a or b to x.

Is it recommended to nest ternary operators?

A Only if you use parentheses

B Yes, always for clarity

C No, it can make code hard to read

D Only in comments

Nesting ternary operators is allowed but can make code difficult to understand.

What is the main advantage of using the ternary operator?

A It creates new variables

B It replaces loops

C It makes code longer

D It shortens simple if-else statements

The ternary operator shortens simple if-else statements into one line.

Explain how the ternary operator works and write a simple example.

Think of it as a shortcut for if-else.

Describe when you might choose to use the ternary operator instead of a full if-else statement.

Consider short and clear code.

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