How do I use the strconv.Atoi() method in Go?

Question

I am trying to get a user input in this small program. I have tried doing this several ways with the strconv.Atoi() method (my input is obviously a string, and I'm trying to convert it to an integer). Here's my first attempt:

package main
    import (
        "fmt"
        "strconv"
    )
    
    func main() {
        //fmt.Println(strconv.Itoa)
        fmt.Println("Say something, in numbers.")
        var inputstr string
        fmt.Scanln("%s", &inputstr)
        input := strconv.Atoi(inputstr)
        output := (input * 2)
        outputstr := strconv.Itoa(output)
        fmt.Println(outputstr)
    }

and got the following error when it came to compiling:

(line 19) multiple-value strconv.Atoi() in single-value context

I then looked into Godocs and tried to figure this out for myself, and then realized that an error value is returned as well. So, I changed the

input := strconv.Atoi(inputstr)

to

input, _ := strconv.Atoi(inputstr)

Now this compiles just fine, without any errors. However, when I run the program, here's what I get:

Say something, in numbers.

0

and then it exits... What am I doing wrong? I believe this is a question about to Atoi() method, but if it's concerning the Scanln() then please correct me.

Answer 1

The problem turns out to be the Scanln. Scanln is returning an error type not a pointer because of the %s. This then leaves inputstr blank, which when given to Atoi is returning an error: strconv.ParseInt: parsing "": invalid syntax.

Using Scanf as follows with no change to the Atoi:

func main() {
    //fmt.Println(strconv.Itoa)
    fmt.Println("Say something, in numbers.")
    var inputstr string

    //fmt.Scanln("%s", &inputstr)
    _, err := fmt.Scanf("%s", &inputstr)
    if err != nil {
        fmt.Println(err)
    }
    input, e := strconv.Atoi(inputstr)
    if e != nil {
        fmt.Println(e)
    }
    output := (input * 2)
    outputstr := strconv.Itoa(output)
    fmt.Println(outputstr)
}

Probably the simplest solution is to remove the "%s" from the Scanln.