Introduction

The factorial of a number is the product of all positive integers less than or equal to that number.
Factorial is commonly denoted by the symbol “n!” where “n” is the number. For example, the factorial
of 5 is 5! = 5 × 4 × 3 × 2 × 1 = 120. Factorial plays a significant role in mathematics, particularly in
combinatorics, probability, and algebra.

Objective

In this program, we aim to calculate the factorial of a given integer using the Go programming language.
The program will ask for user input, compute the factorial recursively, and display the result.

Go Code: Factorial Calculation

package main

import (
    "fmt"
    "log"
    "strconv"
)

// Factorial function to calculate factorial recursively
func factorial(n int) int {
    if n == 0 || n == 1 {
        return 1
    }
    return n * factorial(n-1)
}

func main() {
    // Taking user input
    var input string
    fmt.Print("Enter a positive integer: ")
    fmt.Scanln(&input)
    
    // Converting input to integer
    num, err := strconv.Atoi(input)
    if err != nil || num < 0 {
        log.Fatal("Please enter a valid positive integer.")
    }

    // Calculating factorial
    result := factorial(num)
    
    // Outputting the result
    fmt.Printf("The factorial of %d is %d\n", num, result)
}
            

Explanation of the Program Structure

This Go program consists of the following key parts:

• Import Statements: The program uses three packages: fmt for input and output, log for error handling, and strconv for string-to-integer conversion.
• Factorial Function: A recursive function factorial(n int) int that calculates the factorial of a given integer. If n is 0 or 1, it returns 1 (base case); otherwise, it recursively calls itself with n-1.
• Input Handling: The program asks the user to input a positive integer and checks if the input is valid. If not, it stops execution and prints an error message.
• Main Function: This is where the input is taken, the factorial is calculated, and the result is printed to the console.

How to Run the Program

Follow these steps to run the Go program on your machine:

1. Install Go from the official Go website: https://golang.org/dl/
2. Create a new file, for example factorial.go, and copy the code provided above into that file.
3. Open your terminal (Command Prompt, PowerShell, or any shell) and navigate to the directory where the factorial.go file is saved.
4. Run the following command to compile and execute the Go program:

   go run factorial.go

5. The program will prompt you to enter a positive integer. After entering the number, it will calculate and display the factorial.