C Program to Check Evil Number

Posted in C Tutorial

Updated on Jan 11, 2024

By Mari Selvan

👁️ 56 - 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 explore 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 delve into the C code that accomplishes this task.

isEvilNumber.c

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#include <stdio.h>

// 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
int 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))
    printf("%d is an Evil Number.\n", number);
  else
    printf("%d is not an Evil Number.\n", number);

  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.

Compile and run the program to check if the specified number 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.c

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#include <stdio.h>

// Function to check if a number is evil
int isEvil(int num) {
  int binaryOnes = 0;

  while (num > 0) {
    // Count the number of 1s in binary representation
    if (num % 2 == 1) {
      binaryOnes++;
    }
    num /= 2; // Shift right for binary representation
  }

  return binaryOnes % 2 == 0;
}

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

  for (int i = 1; i <= 10; ++i) {
    if (isEvil(i)) {
      printf("%d ", i);
    }
  }

  printf("\n");

  return 0;
}

💻 Testing the Program

Output

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

Run the program to check for Evil Numbers in the range from 1 to 10.

🧠 How the Program Works

The program defines a function isEvil that takes a number as input and returns whether it's an Evil Number.
Inside the function, it counts the number of 1s in the binary representation of the given number.
The main function tests the range from 1 to 10, printing the Evil Numbers found in this range.

🧐 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.