Golang的词法作用域？

I don't quite understand why a is not 2 at the end:

func main (){
    z := 4
    if true {
        z := 2
        fmt.Println(z)
    }
    fmt.Println(z) // prints 4
}

z is getting shadowed. Change := to = and it will work.

func main (){
    z := 4
    if true {
        z = 2
        fmt.Println(z)
    }
    fmt.Println(z) // prints 2
}

The if statement has its own scope, when you used := you declared a new variable and shadowed the old one.

This does not even compile (I was answering the unedited version of the question).

You have to use ; instead of ,:

func main(){
  a := 0
  for i := 0; i < 10; i++ {
    a += 5
  }
  fmt.Println(a) // prints 50
}