 # R Program to check prime number

## How to check the given number is a prime number or not

Here we are explaining how to write an R program to take number from the user and check it is a prime number or not. we can use the `readline()` function to take input from the user (terminal). Here the prompt argument can choose to display an appropriate message for the user. A positive integer greater than 1 has no other factors except 1 and the number itself is called a prime number.

Numbers 2, 3, 5, 7, 11, 13, etc. are prime numbers as they do not have any other factors.

But, 6 is not prime (it is composite) since, 2 x 3 = 6.

## How prime number check is implemented in R Program

We are using `readline()` function for taking the user's input. Given below are the steps which are used in the R program to read value for prime check. In this R program, we accept the user's values into num by providing an appropriate message to the user using '`prompt`'. Check the given number is greater than 1 because prime numbers must be greater than one. Check if num is exactly divisible by any number from 2 to num – 1 and find a factor in that range then set flag=0 otherwise flag=1. Print the message as a number is a prime number if the flag=1 otherwise the number is not prime.

## ALGORITHM

STEP 1: prompting appropriate messages to the user

STEP 2: take user input using `readline()` into variables num

STEP 3: set flag=0 at first

STEP 4:check if the num is greater than 1 or not if yes set flag=1

STEP 5:check if num is exactly divisible by any number from 2 to num – 1

STEP 6:If we find a factor in that range set flag=0

STEP 7:if flag=1 print number is a prime number

STEP 8:else if flag=0 print number is not a prime number

## R Source Code

```                                          ```num = as.integer(readline(prompt = "Enter a number: "))
flag = 0
if (num > 1) {
flag = 1
for (i in 2: (num - 1)) {
if ((num %% i) == 0) {
flag = 0
break
}
}
}
if (num == 2) flag = 1
if (flag == 1) {
print(paste(num, "is a prime number"))
} else {
print(paste(num, "is not a prime number"))
}```
```

## OUTPUT

```Enter a number: 15
 "15 is not a prime number"

Enter a number: 13
 "13 is a prime number"```
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