R Program to Find the Factorial of a Number

The factorial of a number is the product of all the integers from 1 to that number. For example, the factorial of 6 (denoted as 6!) is 1*2*3*4*5*6 = 720.

Factorial is not defined for negative numbers and the factorial of zero is one, 0! = 1.

This example finds the factorial of a number normally. However, you can find it using recursion as well.

Learn more about how you can find the factorial of a number using recursion.

Example: Find the factorial of a number

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

Output

Enter a number: 8
[1] "The factorial of 8 is 40320"

Here, we take input from the user and check if the number is negative, zero or positive using if...else statement.

If the number is positive, we use for loop to calculate the factorial.

We can also use the built-in function factorial() for this.

> factorial(8)
[1] 40320