 # R Program to find the factorial of a number

## How to find the factorial of a number

Here we are explaining how to write an R program to find the factorial of a number. 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.

## How factorial calculation 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 find the factorial of a number. In this R program, we accept the user's input into the variable number by providing an appropriate message to the user using '`prompt`'. The factorial of a number is the product of all the integers from 1 to that number. The factorial of zero is one and Factorial is not defined for negative numbers.

## ALGORITHM

STEP 1: prompting appropriate messages to the user

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

STEP 3: check if the number is negative, zero, or positive using `if...else` statement

STEP 4:If the number is positive, we use `for loop` to calculate the factorial

STEP 5:print the result

## R Source Code

```                                          ```number = as.integer(readline(prompt="Enter a number: "))
factorial = 1
# check is the number is negative, positive or zero
if(number < 0) {
print("Sorry, factorial does not exist for negative numbers")
} else if(number == 0) {
print("The factorial of 0 is 1")
} else {
for(i in 1:number) {
factorial = factorial * i
}
print(paste("The factorial of", number ,"is",factorial))
```
```

## OUTPUT

```Enter a number: 8
 "The factorial of 8 is 40320"```
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