GO Program to Find Factorial of a Number

//Program to find Factorial of number
package main
import "fmt"

/* Variable Declaration */
var factVal uint64 = 1 // uint64 is the set of all unsigned 64-bit integers.
                       // Range: 0 through 18446744073709551615. 
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++ {
            factVal *= uint64(i)  // mismatched types int64 and int
        }
        
    }    
    return factVal  /* return from function*/
}

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