Factorial in Every Language

Published on 01 November 2018 (Updated: 02 May 2020)

Factorial in Every Language

The factorial of an integer n is defined as:

n! = 1 x 2 x 3 x 4 x ... x n

With the special case 0! = 1.

Requirements

You must write an executable program that accepts an integer n on standard input via the command line, and outputs n! to standard output.

Note that the factorial function grows very quickly. For example, 4! = 24 but 8! = 40320. Therefore, you should impose a limit on the input, so that the largest factorial still fits into your language’s largest supported datatype.

Also note that the factorial is not defined for negative integers.

Testing

Some tests for your program are:

Description Input Output
No input   “Usage: please input a non-negative integer”
Empty input ”” “Usage: please input a non-negative integer”
Invalid Input: Not a number “asdf” “Usage: please input a non-negative integer”
Invalid Input: Negative integer -1 “Usage: please input a non-negative integer”
Sample Input: Zero 0 1
Sample Input: One 1 1
Sample Input: Four 4 24
Sample Input: Eight 8 40320
Sample Input: Ten 10 3628800

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