Conditional Operator in C

The conditional operator allows a program to select one of two expressions depending on whether a condition is true or false.

int age = 20;

char *result = (age >= 18) ? "Adult" : "Minor";

printf("%s", result);

Output:

Adult

The conditional operator is called the ternary operator because it operates on three operands:

1. A condition
2. The expression selected when the condition is true
3. The expression selected when the condition is false

condition ? true_expression : false_expression;

condition ? expression1 : expression2;

The question mark ? separates the condition from the true expression, while the colon : separates the true and false expressions.

int number = 10;

int result = (number > 5) ? 100 : 200;

The condition number > 5 is true, so 100 is selected and assigned to result.

result = 100

int age = 20;

int result = (age >= 18) ? 1 : 0;

printf("%d", result);

Output:

1

Because the age is at least 18, the first expression is selected.

int a = 10;
int b = 20;

int larger = (a > b) ? a : b;

printf("%d", larger);

Output:

20

The operator selects the larger value.

int a = 10;
int b = 20;

int smaller = (a < b) ? a : b;

printf("%d", smaller);

Output:

10

int marks = 75;

char *result = (marks >= 40) ? "Pass" : "Fail";

printf("%s", result);

Output:

Pass

The conditional operator selects one of the two string literals.

int number = 7;

char *result = (number % 2 == 0) ? "Even" : "Odd";

printf("%s", result);

Output:

Odd

The remainder operator is used to create the condition.

int number = -5;

char *result = (number >= 0) ? "Positive" : "Negative";

printf("%s", result);

Output:

Negative

This example treats zero as non-negative.

int age = 25;

int status;

status = (age >= 18) ? 1 : 0;

printf("%d", status);

Output:

1

int age = 16;

printf("%s", (age >= 18) ? "Adult" : "Minor");

Output:

Minor

The selected expression is passed directly to printf().

Using if-else:

if (age >= 18)
{
    result = 1;
}
else
{
    result = 0;
}

Using the conditional operator:

result = (age >= 18) ? 1 : 0;

The conditional operator can make a simple two-choice assignment more compact.

#include <stdio.h>

int main()
{
    int number;

    printf("Enter a number: ");
    scanf("%d", &number);

    printf("%s", (number % 2 == 0) ? "Even" : "Odd");

    return 0;
}

The program takes a number and directly displays whether it is even or odd.

#include <stdio.h>

int main()
{
    int marks;

    printf("Enter marks: ");
    scanf("%d", &marks);

    printf("%s", (marks >= 40) ? "Pass" : "Fail");

    return 0;
}

The condition checks whether the marks are at least 40.

#include <stdio.h>

int main()
{
    int a = 50;
    int b = 80;

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

    printf("Maximum = %d", max);

    return 0;
}

Output:

Maximum = 80

#include <stdio.h>

int main()
{
    int a = 50;
    int b = 80;

    int min = (a < b) ? a : b;

    printf("Minimum = %d", min);

    return 0;
}

Output:

Minimum = 50

float a = 10.5f;
float b = 20.5f;

float result = (a > b) ? a : b;

printf("%.2f", result);

Output:

20.50

The conditional operator can also select between floating-point values.

char grade1 = 'A';
char grade2 = 'B';

char result = (grade1 < grade2) ? grade1 : grade2;

printf("%c", result);

The operator can select one of two compatible character values.

A conditional operator can be placed inside another conditional expression. This is called a nested conditional operator.

int marks = 75;

char *grade =
    (marks >= 80) ? "A" :
    (marks >= 60) ? "B" :
    (marks >= 40) ? "C" : "F";

printf("%s", grade);

Output:

B

Nested conditional expressions should be used carefully because too many levels can make code difficult to read.

int age = 25;
int marks = 70;

char *result =
    (age >= 18 && marks >= 40) ? "Eligible" : "Not Eligible";

printf("%s", result);

Logical and relational operators can be used inside the condition.

int value = 0;

char *result = value ? "True" : "False";

printf("%s", result);

Output:

False

In a condition, zero is treated as false.

int value = 10;

char *result = value ? "True" : "False";

printf("%s", result);

Output:

True

In a condition, a nonzero value is treated as true.

int price = 500;
int discount = 1;

int finalPrice = discount ? price - 50 : price;

printf("Final Price = %d", finalPrice);

Output:

Final Price = 450

The selected expression becomes the value assigned to finalPrice.

int number = -15;

int absolute = (number < 0) ? -number : number;

printf("%d", absolute);

Output:

15

The operator chooses the appropriate expression based on whether the number is negative.

• Forgetting the ? symbol.
• Forgetting the : symbol.
• Using more than two result expressions without proper nesting.
• Confusing ? with other operators.
• Making nested conditional expressions too complicated.
• Using expressions with incompatible types without understanding the resulting type.
• Using the conditional operator where a longer if-else statement would be clearer.

int a = 10;
int b = 20;

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

printf("%d", result);

Parentheses around the condition are commonly used to make the condition easy to read.

The entire conditional expression can also be placed inside a larger expression when appropriate.

#include <stdio.h>

int main()
{
    int a, b;

    printf("Enter first number: ");
    scanf("%d", &a);

    printf("Enter second number: ");
    scanf("%d", &b);

    int maximum = (a > b) ? a : b;
    int minimum = (a < b) ? a : b;

    printf("Maximum = %d\n", maximum);
    printf("Minimum = %d\n", minimum);

    return 0;
}

This program uses the conditional operator to find both the maximum and minimum of two numbers.

Using if-else:

int number = 10;
int result;

if (number > 0)
{
    result = 1;
}
else
{
    result = 0;
}

Using conditional operator:

int number = 10;

int result = (number > 0) ? 1 : 0;

Both approaches can produce the same result. The conditional operator is particularly useful for short expressions with two alternatives.

Practice the following programs:

1. Check whether a number is even or odd.
2. Check whether a number is positive or negative.
3. Find the larger of two numbers.
4. Find the smaller of two numbers.
5. Check whether a student has passed.
6. Check whether a person is an adult or minor.
7. Find the maximum of two values.
8. Find the minimum of two values.
9. Calculate a discounted price using the conditional operator.
10. Create a grade system using nested conditional operators.

Practice simple conditions first. Once you understand the basic syntax, you can use the conditional operator with calculations and multiple conditions.