Check Prime number with While loop in R

R Programming: Control Structure Exercise-5 with Solution

Write a R program function to check if a given number is prime using a while loop.

Sample Solution :

R Programming Code :

# Define a function to check if a given number is prime
is_prime <- function(n) {
    # Base case: if the number is less than 2, it's not prime
    if (n < 2) {
        return(FALSE)  # Return FALSE for numbers less than 2
    }
    
    # Initialize divisor and counter
    divisor <- 2  # Start checking divisibility from 2
    counter <- 0  # Initialize counter to 0
    
    # Continue loop until divisor squared is greater than or equal to n
    while (divisor * divisor <= n) {
        # If n is divisible by the current divisor, it's not prime
        if (n %% divisor == 0) {
            return(FALSE)  # Return FALSE if n is divisible by divisor
        }
        
        # Increment divisor
        divisor <- divisor + 1  # Move to the next divisor
    }
    
    # If the loop completes without finding a divisor, n is prime
    return(TRUE)  # Return TRUE if no divisor found
}

# Test the function with example inputs
test_number <- 37  # Example input to test if it's prime
is_test_prime <- is_prime(test_number)  # Call the is_prime function

# Print the result
if (is_test_prime) {
    cat(test_number, "is prime.\n")  # Print if the number is prime
} else {
    cat(test_number, "is not prime.\n")  # Print if the number is not prime
}

Output:

37 is prime.                  

Explatnaion:

In the exercise above,

• Define the function "is_prime":
• This function takes a single parameter 'n', representing the number to check for primality.
• Base Case:
• If the input number 'n' is less than 2, it's not prime, so the function returns 'FALSE'.
• Initialization:
• 'divisor' is initialized to 2, as we start checking for divisibility from 2 onwards.
• 'counter' is initialized to 0.
• While loop:
• The while loop continues until the square of 'divisor' is greater than or equal to 'n'.
• Inside the loop, it checks if 'n' is divisible by the current 'divisor'. If it is, the function immediately returns 'FALSE', indicating that 'n' is not prime.
• Result:
• If the loop completes without finding a divisor, it means that 'n' is prime, and the function returns 'TRUE'.
• Testing the function:
• The function is tested with an example input ('test_number'), and the result is stored in 'is_test_prime'.

R Programming Code Editor:

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