Factorial Calculation in Go

This program calculates the factorial of a given number using the Go programming language.

What is a Factorial?

The factorial of a non-negative integer n is the product of all positive integers less than or equal to n.
It is denoted by n! and is defined as:

        n! = n * (n-1) * (n-2) * ... * 1

For example, 5! = 5 * 4 * 3 * 2 * 1 = 120.

Go Program to Calculate Factorial

// Package main implements a simple program to calculate the factorial of a given number.
package main

import (
    "fmt"
)

// factorial function computes the factorial of a given non-negative integer n.
// If n is 0, it returns 1 because 0! is defined to be 1.
// It returns the factorial of n otherwise.
func factorial(n int) int {
    if n == 0 {
        return 1
    }
    return n * factorial(n-1)
}

// main function is the entry point of the program.
// It prompts the user to enter a number and calculates its factorial.
func main() {
    var num int
    fmt.Print("Enter a number to calculate its factorial: ")
    fmt.Scan(&num)
    
    if num < 0 {
        fmt.Println("Factorial is not defined for negative numbers.")
    } else {
        result := factorial(num)
        fmt.Printf("The factorial of %d is %d.\n", num, result)
    }
}
    

Explanation

• package main: Defines the main package of the Go program.
• import "fmt": Imports the fmt package for formatted I/O.
• func factorial(n int) int: Defines a recursive function to calculate the factorial of a non-negative integer n.
  • If n is 0, it returns 1 since 0! = 1.
  • Otherwise, it returns n multiplied by the factorial of n-1.
• func main(): The main function, which is the entry point of the program.
  • Prompts the user to enter a number.
  • Reads the input number.
  • If the number is negative, it prints an error message since factorials are not defined for negative numbers.
  • If the number is non-negative, it calculates the factorial by calling the factorial function and prints the result.