Relational operators in C++

Introduction

Relational operators help us compare two values to see how they relate to each other, like if one is bigger or smaller.

Checking if a number is greater than another to decide what to do next.

Comparing ages to see who is older.

Finding out if two values are equal before continuing a task.

Determining if a score is less than a passing mark.

Seeing if a temperature is within a safe range.

Syntax

C++

value1 < value2
value1 > value2
value1 <= value2
value1 >= value2
value1 == value2
value1 != value2

Use == to check if two values are equal, not = which assigns a value.

Relational operators return true or false (boolean values).

Examples

This checks if a is less than b. It is true because 5 is less than 10.

C++

int a = 5;
int b = 10;
bool result = a < b;  // true

This checks if x is equal to y. It is true because both are 7.

C++

int x = 7;
int y = 7;
bool result = x == y;  // true

This checks if m is not equal to n. It is true because 3 is not 8.

C++

int m = 3;
int n = 8;
bool result = m != n;  // true

Sample Program

This program compares two ages using relational operators and prints the results as 1 (true) or 0 (false).

C++

#include <iostream>
using namespace std;

int main() {
    int age1 = 20;
    int age2 = 25;

    cout << "Is age1 less than age2? " << (age1 < age2) << "\n";
    cout << "Is age1 equal to age2? " << (age1 == age2) << "\n";
    cout << "Is age1 not equal to age2? " << (age1 != age2) << "\n";

    return 0;
}

Important Notes

Relational operators always return a boolean value: true or false.

In C++, true prints as 1 and false prints as 0 when using cout.

Be careful to use == for comparison, not = which is for assignment.

Summary

Relational operators compare two values and return true or false.

They include <, >, <=, >=, ==, and !=.

Use them to make decisions based on how values relate to each other.

Practice

1.

Which of the following relational operators checks if two values are not equal in C++?

easy

A. >=

B. !=

C. <=

D. ==

Solution

1. Step 1: Understand the meaning of each operator

   The operator == checks equality, <= and >= check less or equal and greater or equal respectively.

2. Step 2: Identify the operator for 'not equal'

   The operator != means 'not equal' in C++.

3. Final Answer:

   != -> Option B

4. Quick Check:

   Not equal operator = != [OK]

Hint: Remember: != means not equal in C++ [OK]

Common Mistakes:

• Confusing == with !=
• Thinking <= means not equal
• Mixing up >=
• Using = instead of ==

2.

Which of the following is the correct syntax to compare if a is greater than b in C++?

int a = 5, b = 3;
if (___) {
    // code
}

easy

A. a > b

B. a => b

C. a >< b

D. a >= b

Solution

1. Step 1: Recall the correct operator for 'greater than'

   The operator for 'greater than' is >. The operator >= means 'greater than or equal to'.

2. Step 2: Check syntax correctness

   a > b is the correct syntax to check if a is strictly greater than b. Other options are invalid syntax.

3. Final Answer:

   a > b -> Option A

4. Quick Check:

   Greater than operator = > [OK]

Hint: Use > for greater than, >= for greater or equal [OK]

Common Mistakes:

• Using => instead of >=
• Using >< which is invalid
• Confusing >= with >
• Missing spaces causing syntax errors

3.

What will be the output of the following C++ code?

int x = 7, y = 10;
if (x <= y) {
    std::cout << "Yes";
} else {
    std::cout << "No";
}

medium

A. No

B. 10

C. 7

D. Yes

Solution

1. Step 1: Evaluate the relational expression

   Check if x <= y means 7 is less than or equal to 10, which is true.

2. Step 2: Determine which branch executes

   Since the condition is true, the if block runs and prints "Yes".

3. Final Answer:

   Yes -> Option D

4. Quick Check:

   7 <= 10 is true, so output is Yes [OK]

Hint: Check condition truth to decide output [OK]

Common Mistakes:

• Confusing <= with <
• Assuming else block runs
• Printing variable values instead of strings
• Ignoring the condition result

4.

Find the error in the following C++ code snippet:

int a = 4, b = 9;
if (a = b) {
    std::cout << "Equal";
} else {
    std::cout << "Not Equal";
}

medium

A. Incorrect variable declaration

B. Missing semicolon after if statement

C. Using assignment operator instead of equality operator in if condition

D. Using std::cout incorrectly

Solution

1. Step 1: Identify the operator in the if condition

   The condition uses a = b, which assigns value of b to a instead of comparing.

2. Step 2: Correct the operator for comparison

   To compare, the operator should be ==, so the condition should be a == b.

3. Final Answer:

   Using assignment operator instead of equality operator in if condition -> Option C

4. Quick Check:

   Use == for comparison, not = [OK]

Hint: Use == to compare, = to assign [OK]

Common Mistakes:

• Using = instead of ==
• Forgetting to compare variables
• Assuming assignment returns boolean false
• Ignoring compiler warnings

5.

Given the code below, what will be the output?

int a = 5, b = 5, c = 10;
if (a == b && c > b) {
    std::cout << "Match";
} else if (a != b || c < b) {
    std::cout << "Mismatch";
} else {
    std::cout << "Unknown";
}

hard

A. Match

B. Unknown

C. Mismatch

D. Compilation error

Solution

1. Step 1: Evaluate the first if condition

   Check a == b (5 == 5) is true, and c > b (10 > 5) is true, so the whole condition is true.

2. Step 2: Determine which block executes

   Since the first condition is true, "Match" is printed and the rest is skipped.

3. Final Answer:

   Match -> Option A

4. Quick Check:

   Both conditions true, so output is Match [OK]

Hint: Check && needs both true, || needs one true [OK]

Common Mistakes:

• Confusing && and || operators
• Ignoring short-circuit evaluation
• Assuming else if runs after true if
• Misreading relational comparisons