Relational operators in C - Mini Project: Build & Apply

Relational Operators in C

📖 Scenario: You are creating a simple program to compare ages of two friends to see who is older.

🎯 Goal: Build a C program that uses relational operators to compare two age values and prints the comparison results.

📋 What You'll Learn

Create two integer variables named age1 and age2 with exact values 25 and 30

Create an integer variable named isOlder to store the result of the comparison

Use the relational operator > to check if age1 is greater than age2

Print the value of isOlder to show the comparison result

💡 Why This Matters

🌍 Real World

Comparing values is common in programs that make decisions, like checking ages, prices, or scores.

💼 Career

Understanding relational operators is essential for writing conditions in software development, testing, and data validation.

1

Create age variables

Create two integer variables called age1 and age2 with values 25 and 30 respectively.

C

// Your code here

Hint

Use int to declare variables and assign the exact values.

2

Create comparison variable

Create an integer variable called isOlder to store the result of comparing if age1 is greater than age2.

C

#include 

int main() {
    int age1 = 25;
    int age2 = 30;
    // Your code here
    return 0;
}

Hint

Declare isOlder as an integer without assigning a value yet.

3

Compare ages using relational operator

Assign to isOlder the result of the expression age1 > age2 using the relational operator >.

C

#include 

int main() {
    int age1 = 25;
    int age2 = 30;
    int isOlder;
    // Your code here
    return 0;
}

Hint

Use the relational operator > to compare age1 and age2.

4

Print the comparison result

Use printf to print the value of isOlder so the program shows 0 or 1 depending on the comparison.

C

#include 

int main() {
    int age1 = 25;
    int age2 = 30;
    int isOlder;
    isOlder = age1 > age2;
    // Your code here
    return 0;
}

Hint

Use printf("%d\n", isOlder); to print the integer value with a new line.

Practice

1. Which of the following relational operators in C checks if two values are equal?

easy

A. !=

B. ==

C. =

D. >

Solution

1. Step 1: Understand the purpose of each operator

   The operator == is used to compare two values for equality. The single = is an assignment operator, != checks inequality, and > checks if left is greater than right.

2. Step 2: Identify the equality operator

   Since == compares two values for equality, it is the correct relational operator for this purpose.

3. Final Answer:

   == -> Option B

4. Quick Check:

   Equality check = == [OK]

Hint: Equality uses double equals ==, not single = [OK]

Common Mistakes:

• Confusing = (assignment) with == (equality)
• Using != instead of ==
• Using > instead of ==

2. Which of the following is the correct syntax to check if variable a is not equal to variable b in C?

easy

A. a !== b

B. a <> b

C. a =! b

D. a != b

Solution

1. Step 1: Recall the correct not equal operator in C

   In C, the operator for not equal is !=. Other options like <> or !== are not valid in C.

2. Step 2: Verify the syntax correctness

   The expression a != b correctly compares if a is not equal to b.

3. Final Answer:

   a != b -> Option D

4. Quick Check:

   Not equal operator = != [OK]

Hint: Use != for not equal in C, not <> or !== [OK]

Common Mistakes:

• Using <> which is invalid in C
• Writing =! instead of !=
• Using !== which is from other languages

3. What will be the output of the following C code?

int a = 5, b = 10;
if (a > b) {
    printf("True\n");
} else {
    printf("False\n");
}

medium

A. True

B. 5

C. False

D. 10

Solution

1. Step 1: Evaluate the relational expression a > b

   Variable a is 5 and b is 10. Since 5 is not greater than 10, the expression a > b is false.

2. Step 2: Determine which branch executes

   Because the condition is false, the else block runs, printing "False".

3. Final Answer:

   False -> Option C

4. Quick Check:

   5 > 10 = false [OK]

Hint: Compare values carefully; 5 > 10 is false [OK]

Common Mistakes:

• Assuming 5 > 10 is true
• Confusing else and if blocks
• Ignoring relational operator meaning

4. Identify the error in the following C code snippet:

int x = 7, y = 3;
if (x =< y) {
    printf("x is less or equal to y\n");
}

medium

A. Using =< instead of <=

B. Missing semicolon after if condition

C. Using assignment operator inside if

D. Incorrect printf syntax

Solution

1. Step 1: Check the relational operator syntax

   The operator =< is invalid in C. The correct operator for less than or equal is <=.

2. Step 2: Confirm other syntax correctness

   The semicolon after if condition is not needed, assignment operator is not used here, and printf syntax is correct.

3. Final Answer:

   Using =< instead of <= -> Option A

4. Quick Check:

   Less or equal operator is <=, not =< [OK]

Hint: Remember <= for less or equal, not =< [OK]

Common Mistakes:

• Swapping <= to =<
• Adding semicolon after if condition
• Confusing assignment = with comparison ==

5. Given the code below, what will be the output?

int a = 4, b = 4, c = 5;
if (a == b && b < c) {
    printf("Yes\n");
} else {
    printf("No\n");
}

Choose the correct output considering relational operators combined with logical operators.

hard

A. Yes

B. No

C. 4

D. Syntax Error

Solution

1. Step 1: Evaluate the first condition a == b

   Both a and b are 4, so a == b is true.

2. Step 2: Evaluate the second condition b < c

   b is 4 and c is 5, so b < c is true.

3. Step 3: Combine conditions with logical AND

   Both conditions are true, so the combined condition is true, executing the if block.

4. Final Answer:

   Yes -> Option A

5. Quick Check:

   (4 == 4) && (4 < 5) = true [OK]

Hint: Both conditions must be true for && to print Yes [OK]

Common Mistakes:

• Ignoring logical AND meaning
• Mixing up == and =
• Assuming false when both conditions true