Equality Operator (==) in C++

The equality operator (==) in C++ is used to compare two values or expressions to check whether they are equal. If the values are the same, the result is true; otherwise, it’s false.

This operator is widely used in conditions, control structures, validations, loops, and logical expressions.

Syntax

operand1 == operand2

• Returns true (1) if both operands are equal.
• Returns false (0) if they are not equal.

1. Equality with Integers

int a = 10, b = 10;
std::cout << (a == b);  // Output: 1 (true)

2. Equality with Float and Double

Due to floating-point precision issues, direct comparison can sometimes be inaccurate.

float x = 3.14f;
float y = 3.14f;
std::cout << (x == y);  // Output: 1 (true)

double a = 0.1 + 0.2;
double b = 0.3;
std::cout << (a == b);  // Output: 0 (false)

For reliable floating-point comparison, use a tolerance value (epsilon):

#include <cmath>
bool isEqual = std::abs(a - b) < 1e-9;
std::cout << isEqual;  // Output: 1 (true)

3. Equality with Characters

char a = 'A', b = 'A';
std::cout << (a == b);  // Output: 1 (true)

You can also compare characters with their ASCII values:

char ch = 'B';
std::cout << (ch == 66);  // Output: 1 (true)

4. Equality with Boolean

bool status = true;
std::cout << (status == true);  // Output: 1 (true)

5. Equality with Strings (C++ string class)

#include <string>
std::string name1 = "Alice";
std::string name2 = "Alice";
std::cout << (name1 == name2);  // Output: 1 (true)

6. Equality with C-style strings (Character arrays)

C-style strings require strcmp() from <cstring> for accurate comparison.

#include <cstring>
char a[] = "hello";
char b[] = "hello";
std::cout << (strcmp(a, b) == 0);  // Output: 1 (true)

7. Equality in Conditions

int age = 18;
if (age == 18) {
    std::cout << "You are 18.";
}

8. Equality with Different Data Types

When comparing different data types, C++ performs implicit type conversions:

int a = 5;
float b = 5.0;
std::cout << (a == b);  // Output: 1 (true)

9. Equality in Loops

int i = 0;
while (i == 0) {
    std::cout << "Still zero\n";
    i++;
}

10. Common Mistake: Using = Instead of ==

Always remember:

• = is assignment
• == is comparison

// if (a = b)  // ❌ This assigns b to a, not compares

Correct usage:

if (a == b)  // ✅ Correct comparison

11. Practice Problems

Problem 1: Are Two Numbers Equal?

int x = 10, y = 15;
if (x == y)
    std::cout << "Equal";
else
    std::cout << "Not Equal";

Problem 2: Is Input Character a Vowel?

char ch = 'e';
if (ch == 'a' || ch == 'e' || ch == 'i' || ch == 'o' || ch == 'u')
    std::cout << "Vowel";
else
    std::cout << "Not a vowel";

Problem 3: Login Validation

std::string inputUsername = "admin";
std::string storedUsername = "admin";
if (inputUsername == storedUsername)
    std::cout << "Login Successful";
else
    std::cout << "Invalid Credentials";

Summary Table

Best Practices

• Use == only for comparison, not assignment.
• Be cautious comparing floating-point values directly.
• For C-style strings, prefer strcmp() or convert them to std::string.
• Use parentheses to group comparisons clearly in complex expressions.