Unraveling the Mysteries of Prime Numbers: A Deep Dive into Function Approaches

The Enigmatic World of Functions

Functions are the building blocks of programming, and understanding how to craft them effectively is crucial for any aspiring developer. In our examples, we’ll create user-defined functions that take input from the user, check if it’s a prime number, and display the result. But here’s the twist: each function will be designed differently, showcasing various techniques to achieve the same goal.

Approach 1: The Void Function

Our first function, checkPrimeNumber(), takes no arguments and returns no value. It’s a self-contained unit that prompts the user for input, checks if it’s prime, and displays the result. This approach is straightforward, but it limits the function’s reusability.

function checkPrimeNumber() {
  const userInput = prompt("Enter a number:");
  let isPrime = true;
  if (userInput <= 1) {
    isPrime = false;
  } else {
    for (let i = 2; i * i <= userInput; i++) {
      if (userInput % i === 0) {
        isPrime = false;
        break;
      }
    }
  }
  alert(`${userInput} is ${isPrime? "" : "not "}a prime number.`);
}

Approach 2: The Return Value

In our second example, getInteger() takes no arguments but returns a value. This function is responsible for getting user input and passing it back to the main function, which then checks if it’s prime. This approach separates concerns, making the code more modular.

function getInteger() {
  return parseInt(prompt("Enter a number:"));
}

function checkPrime(number) {
  let isPrime = true;
  if (number <= 1) {
    isPrime = false;
  } else {
    for (let i = 2; i * i <= number; i++) {
      if (number % i === 0) {
        isPrime = false;
        break;
      }
    }
  }
  alert(`${number} is ${isPrime? "" : "not "}a prime number.`);
}

const userInput = getInteger();
checkPrime(userInput);

Approach 3: Passing Arguments

The checkPrimeAndDisplay() function takes an argument from the user and checks if it’s prime, displaying the result accordingly. This approach is more flexible than the first, as it allows the function to be reused with different inputs.

function checkPrimeAndDisplay(number) {
  let isPrime = true;
  if (number <= 1) {
    isPrime = false;
  } else {
    for (let i = 2; i * i <= number; i++) {
      if (number % i === 0) {
        isPrime = false;
        break;
      }
    }
  }
  alert(`${number} is ${isPrime? "" : "not "}a prime number.`);
}

const userInput = parseInt(prompt("Enter a number:"));
checkPrimeAndDisplay(userInput);

Approach 4: The Ultimate Combo

checkPrimeNumber(), takes an argument from the user and returns a value indicating whether it’s prime or not. This approach is the most robust, as it encapsulates the prime-checking logic within the function and allows for easy reuse.

function checkPrimeNumber(number) {
  let isPrime = true;
  if (number <= 1) {
    isPrime = false;
  } else {
    for (let i = 2; i * i <= number; i++) {
      if (number % i === 0) {
        isPrime = false;
        break;
      }
    }
  }
  return isPrime;
}

const userInput = parseInt(prompt("Enter a number:"));
const isPrime = checkPrimeNumber(userInput);
alert(`${userInput} is ${isPrime? "" : "not "}a prime number.`);

The Verdict: Which Approach Reigns Supreme?

So, which approach is better? The answer lies in the problem you’re trying to solve. In this case, passing an argument and returning a value (Approach 4) is the most effective way to write a reusable and modular function. By separating concerns and encapsulating logic, you’ll write more efficient and maintainable code.

Table of Contents

• Function with no arguments and no return value
• Function with no arguments and a return value
• Function with arguments and no return value
• Function with arguments and a return value
• Which approach is better?