Ternary operator in C

Introduction

The ternary operator lets you choose between two values quickly based on a condition. It makes simple if-else decisions shorter and easier to write.

When you want to assign a value based on a quick yes/no question.

When you want to print one of two messages depending on a condition.

When you want to return a value from a function based on a simple check.

Syntax

C

condition ? value_if_true : value_if_false;

The condition is checked first.

If condition is true, the expression returns value_if_true, otherwise it returns value_if_false.

Examples

Assigns the bigger of a or b to max.

C

int a = 10, b = 20;
int max = (a > b) ? a : b;

Sets result to "Even" if num is even, otherwise "Odd".

C

int num = 5;
char* result = (num % 2 == 0) ? "Even" : "Odd";

Prints "Equal" if a equals b, else prints "Not equal".

C

printf("%s\n", (a == b) ? "Equal" : "Not equal");

Sample Program

This program checks if age is 18 or more. If yes, it sets can_vote to "Yes", otherwise "No". Then it prints the answer.

C

#include <stdio.h>

int main() {
    int age = 18;
    char* can_vote = (age >= 18) ? "Yes" : "No";
    printf("Can vote? %s\n", can_vote);
    return 0;
}

Important Notes

The ternary operator is a shortcut for simple if-else statements.

Use it only for simple conditions to keep code readable.

Both value_if_true and value_if_false must be expressions that return a value.

Summary

The ternary operator chooses between two values based on a condition.

It is written as condition ? value_if_true : value_if_false.

Use it to make your code shorter and clearer for simple decisions.

Practice

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

easy

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

B. It creates a loop that runs twice.

C. It declares a new variable.

D. It comments out code.

Solution

1. Step 1: Understand the ternary operator structure

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

2. Step 2: Determine 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 A

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 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 B

4. Quick Check:

   Syntax is 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 = 5;
int y = (x > 3) ? 10 : 20;
printf("%d", y);

medium

A. 10

B. 20

C. 5

D. Syntax error

Solution

1. Step 1: Evaluate the condition (x > 3)

   Since x is 5, 5 > 3 is true.

2. Step 2: Apply ternary operator

   Because condition is true, y is assigned 10.

3. Final Answer:

   10 -> Option A

4. Quick Check:

   (5 > 3) ? 10 : 20 = 10 [OK]

Hint: Check if condition is true, then pick first value [OK]

Common Mistakes:

• Choosing the false value by mistake
• Confusing variable values
• Thinking it causes syntax error

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

int a = 10;
int b = 20;
int max = a > b ? a, b;

medium

A. Missing colon ':' between values

B. Incorrect variable declaration

C. No error, code is correct

D. Using comma instead of colon in ternary

Solution

1. Step 1: Check ternary operator syntax

   The ternary operator requires a colon ':' between the two possible values.

2. Step 2: Identify the mistake

   The code uses a comma ',' instead of a colon ':', which is incorrect syntax.

3. Final Answer:

   Using comma instead of colon in ternary -> Option D

4. Quick Check:

   Ternary needs ':' not ',' [OK]

Hint: Ternary uses ':' not ',' between values [OK]

Common Mistakes:

• Using comma instead of colon
• Forgetting colon entirely
• Assuming code is correct

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

int a = 0;
int b = 5;
int result = (a != 0) ? (b / a) : (b * 2);
printf("%d", result);

hard

A. 0

B. Division by zero error

C. 10

D. 5

Solution

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

   a is 0, so (0 != 0) is false.

2. Step 2: Apply ternary operator

   Since condition is false, result is assigned (b * 2) = 5 * 2 = 10.

3. Final Answer:

   10 -> Option C

4. Quick Check:

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

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

Common Mistakes:

• Assuming division happens causing error
• Ignoring false condition path
• Confusing variable values