C++ Program to Check Evil Number

Posted in C++ Tutorial

Updated on Jan 11, 2024

By Mari Selvan

👁️ 28 - Views

⏳ 4 mins

💬 1 Comment

Photo Credit to CodeToFun

🙋 Introduction

In the realm of programming, understanding the properties of numbers is a fascinating journey. One interesting concept is that of Evil Numbers.

An Evil Number is a non-negative integer that has an even number of '1' bits in its binary representation.

In this tutorial, we will delve into a C++ program designed to check whether a given number is an Evil Number.

The program involves converting the decimal number to its binary representation and counting the number of '1' bits.

📄 Example

Let's dive into the C++ code that accomplishes this task.

isEvilNumber.cpp

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#include <iostream>

// Function to count the number of set bits (1s) in binary representation
int countSetBits(int number) {
  int count = 0;

  while (number) {
    count += number & 1;
    number >>= 1;
  }

  return count;
}

// Function to check if a number is an Evil Number
bool isEvilNumber(int number) {
  // Count the number of set bits in the binary representation
  int setBitsCount = countSetBits(number);

  // If the count of set bits is even, it is an Evil Number
  return setBitsCount % 2 == 0;
}

// Driver program
int main() {
  // Replace this value with the number you want to check
  int number = 15;

  // Call the function to check if the number is an Evil Number
  if (isEvilNumber(number))
    std::cout << number << " is an Evil Number.\n";
  else
    std::cout << number << " is not an Evil Number.\n";

  return 0;
}

💻 Testing the Program

To test the program with different numbers, modify the value of number in the main program.

Output

15 is an Evil Number.

🧠 How the Program Works

The program defines a function countSetBits that takes an integer number as input and returns the count of set bits (1s) in its binary representation.
The function isEvilNumber checks if the count of set bits is even, indicating that the number is an Evil Number.
Inside the main program, replace the value of number with the desired number you want to check.
The program calls the isEvilNumber function and prints the result.

📏 Between the Given Range

Let's explore the C++ code that checks for Evil Numbers in the specified range.

isEvil.cpp

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#include <iostream>
#include <bitset>

// Function to check if a number is Evil
bool isEvil(int num) {
  std::bitset < 8 > binary(num);
  return binary.count() % 2 == 0;
}

// Driver program
int main() {
  std::cout << "Evil numbers in the range 1 to 10:\n";

  for (int i = 1; i <= 10; ++i) {
    if (isEvil(i)) {
      std::cout << i << " ";
    }
  }

  std::cout << std::endl;

  return 0;
}

💻 Testing the Program

Output

Evil numbers in the range 1 to 10:
3 5 6 9 10

Compile and run the program to see the Evil Numbers in the range 1 to 10.

🧠 How the Program Works

The program defines a function isEvil that takes a number as input, converts it to its binary representation, and checks if the count of 1s is even.
The main function iterates through the range from 1 to 10 and prints the Evil Numbers in the specified format.

🧐 Understanding the Concept of Evil Number

Before delving into the code, let's understand the concept of Evil Numbers. An Evil Number is a non-negative integer that has an even number of '1' bits in its binary representation.