strconv
Atoi
err
nil

Converting string to integer - strconv, Atoi

examples/convert-string-to-integer/convert_string_to_integer.go

package main

import (
    "fmt"
    "strconv"
)

func main() {
    var i int
    i, _ = strconv.Atoi("42")
    fmt.Printf("%v %T\n", i, i) // 42 int

    i, _ = strconv.Atoi("0")
    fmt.Printf("%v %T\n", i, i) // 0 int

    i, _ = strconv.Atoi("23\n")
    fmt.Printf("%v %T\n", i, i) // 0 int

    i, _ = strconv.Atoi("17x")
    fmt.Printf("%v %T\n", i, i) // 0 int
}

42 int
0 int
0 int
0 int

In the first two examples the conversion was successful.
In the 3rd and 4th examples it failed.
How can we know?

While internally Go can represent numbers, the communication with the outside world is always using strings. So when we read from a file we always get strings. When we ask the user to type in a number and the user types in a number, we still receive it as a string. For example as the string "42". So we need a way to convert a string that looks like a number to the numeric representation of Go.