golang中整数的阶乘

package main

import "fmt"

var facVal uint64 = 1

var i int = 1
var n int

/* function declaration */

func factorial(n int) uint64  {
    if n < 0 {
        fmt.Print("Factorial of negative number doesn't exist.")
    } else {
        for i := 1; i <= n ; i++  {
            facVal *= uint64(i)
        }
    }
    return facVal

}

func main()  {
    fmt.Println("Enter a positive integer between 0 - 50 : ")
    fmt.Scan(&n)
    fmt.Print("Factorial is: ", factorial(n))
}