C++ Program to find Composite Number

Posted in C++ Tutorial

Updated on Jan 11, 2024

By Mari Selvan

👁️ 487 - Views

⏳ 4 mins

💬 1 Comment

Photo Credit to CodeToFun

🙋 Introduction

In the realm of programming, identifying and working with different types of numbers is a fundamental skill.

A composite number is one that has more than two positive divisors, excluding 1 and itself. In this tutorial, we'll explore a C++ program that efficiently determines whether a given number is composite or not.

📄 Example

Let's dive into the C++ code that checks whether a number is composite or not.

isComposite.cpp

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#include <iostream>

// Function to check if a number is composite
bool isComposite(int number) {
  if (number <= 1) {
    return false;
  }

  for (int i = 2; i <= number / 2; ++i) {
    if (number % i == 0) {
      return true; // Number has a divisor other than 1 and itself
    }
  }

  return false; // Number is not divisible by any number other than 1 and itself
}

// Driver program
int main() {
  // Replace this value with your desired number
  int testNumber = 15;

  if (isComposite(testNumber)) {
    std::cout << testNumber << " is a composite number." << std::endl;
  } else {
    std::cout << testNumber << " is not a composite number." << std::endl;
  }

  return 0;
}

💻 Testing the Program

To test the program with different numbers, replace the value of testNumber in the main function.

Output

15 is a composite number.

Compile and run the program to see if the given number is composite.

🧠 How the Program Works

The program defines a function isComposite that takes a number as input and returns true if the number is composite and false otherwise.
Inside the function, it iterates through numbers from 2 to half of the given number.
If the number is divisible by any of these numbers, it means it has a divisor other than 1 and itself, making it composite.
The main function tests the program with a sample number and prints whether it is composite or not.

📏 Between the Given Range

Let's dive into the C++ code that checks for composite numbers in the specified range.

isComposite.cpp

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#include <iostream>

// Function to check if a number is composite
bool isComposite(int number) {
  if (number <= 1) {
    return false;
  }

  for (int i = 2; i < number; ++i) {
    if (number % i == 0) {
      return true; // Found a divisor other than 1 and itself
    }
  }

  return false; // No divisors other than 1 and itself
}

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

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

  std::cout << std::endl;

  return 0;
}

💻 Testing the Program

Output

Composite numbers in the range 1 to 10 are: 
4 6 8 9 10

Compile and run the program to see the composite numbers in the specified range.

🧠 How the Program Works

The program defines a function isComposite that takes a number as input and returns true if the number is composite, and false otherwise.
Inside the function, it checks for divisors by iterating from 2 to the number - 1.
The main function tests the isComposite function for numbers in the range from 1 to 10 and prints the composite numbers found.

🧐 Understanding the Concept of Composite Numbers

Composite numbers are integers greater than 1 that have divisors other than 1 and themselves.

For example, the number 12 is composite because it can be formed by multiplying 2 and 6 or 3 and 4.

🎢 Optimizing the Program

While the provided program is effective, consider exploring and implementing optimizations for larger numbers, such as checking divisors up to the square root of the number for improved efficiency.

Feel free to incorporate and modify this code as needed for your specific use case. Happy coding!