import (
    "fmt"
    "strconv"
    "strings"
)

//to int
var strNumber = "42"
//the first method
number1, err := strconv.Atoi(strNumber)

//the second method
number2, err := strconv.ParseInt(strNumber, 10, 16)

//to Double and Float
//the first method
var strPi = "3.14"
pi, err := strconv.ParseFloat(strPi, 64)

//the second method
var strHalf = "0,5"
half1, err := strconv.ParseFloat(strHalf, 32)
//half1 is 0
if err != nil {
    fmt.Println(err)
}
strHalf = strings.Replace(strHalf, ",", ".", 1)
half2, _ := strconv.ParseFloat(strHalf, 32)
//half2 is 0.5

fmt.Println("number1 is", number1)
fmt.Println("number2 is", number2)
fmt.Println("pi is", pi)
fmt.Println("half1 is", half1)
fmt.Println("half2 is", half2)