R Program to Check if a Number is Prime

Introduction

A prime number is a natural number greater than 1 that has no positive divisors other than 1 and itself. This guide will walk you through writing an R program that checks whether a given number is prime.

Problem Statement

Create an R program that:

• Prompts the user to enter a number.
• Checks if the number is prime.
• Displays a message indicating whether the number is prime or not.

Example:

• Input: 7
• Output: 7 is a prime number

Solution Steps

1. Read the Number: Use the readline() function to take the number as input from the user.
2. Convert the Input to Numeric: Convert the input from a character string to a numeric value using the as.numeric() function.
3. Check if the Number is Prime: Use a loop and conditional checks to determine if the number has any divisors other than 1 and itself.
4. Display the Result: Use the print() function to display whether the number is prime or not.

R Program

# R Program to Check if a Number is Prime
# Author: https://www.javaguides.net/

# Step 1: Read the number from the user
number <- as.numeric(readline(prompt = "Enter a number: "))

# Step 2: Function to check if a number is prime
is_prime <- function(num) {
  if (num <= 1) {
    return(FALSE)
  }
  if (num == 2) {
    return(TRUE)
  }
  for (i in 2:sqrt(num)) {
    if (num %% i == 0) {
      return(FALSE)
    }
  }
  return(TRUE)
}

# Step 3: Check if the number is prime
if (is_prime(number)) {
  print(paste(number, "is a prime number"))
} else {
  print(paste(number, "is not a prime number"))
}

Explanation

Step 1: Read the Number

• The readline() function prompts the user to enter a number. The input is read as a string, so it is converted to a numeric value using as.numeric().

Step 2: Function to Check if a Number is Prime

• The function is_prime() checks if a number is prime by iterating through possible divisors from 2 to the square root of the number. If any divisor divides the number without leaving a remainder, the function returns FALSE, indicating that the number is not prime. If no divisors are found, the function returns TRUE.

Step 3: Display the Result

• The program checks the result from the is_prime() function and prints whether the number is prime or not.

Output Example

Example:

Enter a number: 7
[1] "7 is a prime number"

Example:

Enter a number: 10
[1] "10 is not a prime number"

Conclusion

This R program demonstrates how to check if a number is prime by implementing a simple algorithm to test divisibility. It covers key programming concepts such as loops, conditional statements, and functions, making it a useful example for beginners learning R programming.