Not Equal Operator (`!=`) in C++

The not equal operator (!=) in C++ is used to compare two values or expressions to check whether they are not equal. It is the logical opposite of the equality operator (==).

If the values are not equal, it returns true (1). If they are equal, it returns false (0).

Syntax

operand1 != operand2

Returns true if operand1 and operand2 are different.
Returns false if they are equal.

1. Not Equal with Integers

not_equal_int.cpp

int a = 10, b = 20;
std::cout << (a != b);  // Output: 1 (true)

2. Not Equal with Float and Double

Be careful when comparing floating-point numbers due to potential precision issues.

not_equal_float.cpp

float x = 3.14f;
float y = 2.71f;
std::cout << (x != y);  // Output: 1 (true)

not_equal_double.cpp

double a = 0.1 + 0.2;
double b = 0.3;
std::cout << (a != b);  // Output: 1 (true, due to precision error)

For precision-safe comparison, use an epsilon:

not_equal_epsilon.cpp

#include <cmath>
bool notEqual = std::abs(a - b) > 1e-9;
std::cout << notEqual;  // Output: 0 (false)

3. Not Equal with Characters

not_equal_char.cpp

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

4. Not Equal with Boolean Values

not_equal_bool.cpp

bool isActive = true;
std::cout << (isActive != false);  // Output: 1 (true)

5. Not Equal with Strings (`std::string`)

not_equal_string.cpp

#include <string>
std::string a = "hello";
std::string b = "world";
std::cout << (a != b);  // Output: 1 (true)

6. Not Equal with C-style Strings

Use strcmp for accurate comparison with character arrays.

not_equal_cstring.cpp

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

7. Not Equal in Conditions

not_equal_if.cpp

int age = 25;
if (age != 18) {
    std::cout << "You are not 18 years old.";
}

8. Not Equal in Loops

not_equal_while.cpp

int i = 0;
while (i != 5) {
    std::cout << i << " ";
    i++;
}

Output: 0 1 2 3 4

9. Mixed Data Type Comparison

not_equal_mixed.cpp

int x = 5;
float y = 5.0f;
std::cout << (x != y);  // Output: 0 (false)

10. Common Use Case: Input Validation

not_equal_validation.cpp

char option;
std::cin >> option;
 
if (option != 'y' && option != 'Y') {
    std::cout << "You did not choose yes.";
}

Practice Problems

Problem 1: Password Check

practice_password.cpp

std::string input = "user123";
std::string correct = "admin";
 
if (input != correct) {
    std::cout << "Incorrect password!";
}

Problem 2: Skip Even Numbers

practice_skip_even.cpp

for (int i = 1; i <= 10; i++) {
    if (i % 2 != 0) {
        std::cout << i << " ";
    }
}

Problem 3: Character Match

practice_char_match.cpp

char userInput = 'b';
 
if (userInput != 'a') {
    std::cout << "Not the letter A.";
}

Summary Table

Data Type	Example	Result
`int`	`5 != 10`	`true`
`float`	`3.1f != 3.1f`	`false`
`double`	`0.1 + 0.2 != 0.3`	`true`
`char`	`'x' != 'y'`	`true`
`bool`	`true != false`	`true`
`string`	`"apple" != "mango"`	`true`
`char[]`	`strcmp(a, b) != 0`	`true`

Best Practices

Use != for inequality checks, especially in conditional logic and loops.
When comparing floating-point values, use a tolerance (epsilon) instead of direct !=.
For C-style strings, always use strcmp(); never compare with != directly.
Use meaningful conditions. For example: if (status != true) is equivalent to if (!status) and is more readable that way.

Equal to Greater than

Not Equal Operator (!=) in C++