Try to fix main.go file using gofmt command and show diff data from gofmt -d example01 command.

        fmt.Printf(HelloWorld("appleboy"))
        fmt.Println("一天就學會 Go 語言")

-       if (a >= 1) { fmt.Println("a >= 1") }
+       if a >= 1 {
+               fmt.Println("a >= 1")
+       }

Fix and save automatically using -w flag: gofmt -w example01

Try to improve code quailty using golint command.

example01/main.go:13:1: exported function HelloWorld should have comment or be unexported
example01/main.go:13:17: don't use underscores in Go names; func parameter user_name should be userName