Relational operators in C with code examples

Relational operators in C are used to compare values and return a result as true (1) or false (0).

These operators allow you to compare variables and expressions, making them essential for decision-making in conditions, loops, and logical expressions.

1. Relational Operators in C

Here are the main relational operators in C:

2. Example: Basic Comparison of Two Variables

In this example, we use each relational operator to compare two integer variables and display the results.

#include <stdio.h>

int main() {
    int a = 10, b = 20;

    printf("a = %d, b = %d\n", a, b);
    printf("a == b: %d\n", a == b);  // Equal to
    printf("a != b: %d\n", a != b);  // Not equal to
    printf("a > b: %d\n", a > b);    // Greater than
    printf("a < b: %d\n", a < b);    // Less than
    printf("a >= b: %d\n", a >= b);  // Greater than or equal to
    printf("a <= b: %d\n", a <= b);  // Less than or equal to

    return 0;
}

Output:

a = 10, b = 20
a == b: 0
a != b: 1
a > b: 0
a < b: 1
a >= b: 0
a <= b: 1

Explanation:

• The relational expressions evaluate to either 1 (true) or 0 (false).
• a == b is false (0) because 10 is not equal to 20.
• a < b is true (1) because 10 is less than 20.

3. Using Relational Operators in if Statements

Relational operators are frequently used in if statements to make decisions based on comparisons.

#include <stdio.h>

int main() {
    int age = 18;

    if (age >= 18) {
        printf("You are eligible to vote.\n");
    } else {
        printf("You are not eligible to vote.\n");
    }

    return 0;
}

In this example:

• age >= 18 checks if age is at least 18.
• If the condition is true, it prints “You are eligible to vote.” Otherwise, it prints “You are not eligible to vote.”

Output (assuming age is 18):

You are eligible to vote.

4. Using Relational Operators in while Loops

Relational operators can be used in loops to control how many times the loop will execute.

#include <stdio.h>

int main() {
    int count = 1;

    printf("Counting from 1 to 5:\n");
    while (count <= 5) {
        printf("%d\n", count);
        count++;
    }

    return 0;
}

In this example:

• count <= 5 is the condition for the while loop.
• The loop continues as long as count is less than or equal to 5.

Output:

Counting from 1 to 5:
1
2
3
4
5

5. Using Relational Operators in Complex Conditions

You can combine multiple relational expressions in complex conditions using logical operators like && (and) and || (or).

#include <stdio.h>

int main() {
    int age = 25;
    float income = 40000;

    if (age >= 18 && income >= 30000) {
        printf("You are eligible for the loan.\n");
    } else {
        printf("You are not eligible for the loan.\n");
    }

    return 0;
}

In this example:

• The condition age >= 18 && income >= 30000 checks if both conditions are true.
• If age is 18 or older and income is at least 30000, it prints “You are eligible for the loan.”

Output (assuming age is 25 and income is 40000):

You are eligible for the loan.

6. Comparing Floating-Point Numbers

When comparing floating-point numbers, precision issues can arise, so it’s best to use a small tolerance value instead of direct comparison.

#include <stdio.h>
#include <math.h>

int main() {
    float x = 0.1 * 10;
    float y = 1.0;
    float epsilon = 0.00001; // Small tolerance for comparison

    if (fabs(x - y) < epsilon) {
        printf("x and y are approximately equal.\n");
    } else {
        printf("x and y are not equal.\n");
    }

    return 0;
}

In this example:

• fabs(x – y) < epsilon checks if the difference between x and y is less than a small tolerance (epsilon), indicating they are approximately equal.
• This method avoids issues due to the limited precision of floating-point numbers.

Output:

x and y are approximately equal.

7. Using Relational Operators in Arrays and Loops

Relational operators are useful when working with arrays, such as finding the maximum or minimum value.

Example: Finding the Maximum Value in an Array

#include <stdio.h>

int main() {
    int numbers[] = {3, 15, 7, 9, 20, 12};
    int max = numbers[0];

    for (int i = 1; i < 6; i++) {
        if (numbers[i] > max) {
            max = numbers[i];
        }
    }

    printf("The maximum value is: %d\n", max);

    return 0;
}

In this example:

• if (numbers[i] > max) checks if each element is greater than the current max.
• If true, max is updated to that element.

Output:

The maximum value is: 20

8. Comparing Characters with Relational Operators

In C, characters are represented by their ASCII values, so you can use relational operators to compare characters.

#include <stdio.h>

int main() {
    char char1 = 'A';
    char char2 = 'B';

    if (char1 < char2) {
        printf("'%c' comes before '%c' in ASCII.\n", char1, char2);
    } else {
        printf("'%c' comes after '%c' in ASCII.\n", char1, char2);
    }

    return 0;
}

In this example:

• The ASCII value of ‘A’ (65) is less than that of ‘B’ (66).
• char1 < char2 evaluates as true.

Output:

'A' comes before 'B' in ASCII.

9. Summary Table of Relational Operators

10. Complete Program Example: Comparing Values

This program takes two integer inputs and uses relational operators to compare them, displaying the results.

#include <stdio.h>

int main() {
    int num1, num2;

    printf("Enter first number: ");
    scanf("%d", &num1);

    printf("Enter second number: ");
    scanf("%d", &num2);

    printf("\nComparison Results:\n");

    printf("%d == %d: %d\n", num1, num2, num

1 == num2);
    printf("%d != %d: %d\n", num1, num2, num1 != num2);
    printf("%d > %d: %d\n", num1, num2, num1 > num2);
    printf("%d < %d: %d\n", num1, num2, num1 < num2);
    printf("%d >= %d: %d\n", num1, num2, num1 >= num2);
    printf("%d <= %d: %d\n", num1, num2, num1 <= num2);

    return 0;
}

Example Input/Output:

For inputs 10 and 20:

Enter first number: 10
Enter second number: 20

Comparison Results:
10 == 20: 0
10 != 20: 1
10 > 20: 0
10 < 20: 1
10 >= 20: 0
10 <= 20: 1

This tutorial covers relational operators in C, showing how to use them in various contexts such as conditions, loops, arrays, and character comparisons.