如何使用fmt.Println（）扩展变量

I can't expand variables with fmt.Println().

package main
import "fmt"
func main(){
  old := 20
  fmt.Println("I'm %g years old.",old)
}

result =>

I'm %g years old.
20

Use Printf not Println. Use %d for old which is type int. Add a newline.

For example,

package main

import "fmt"

func main() {
    old := 20
    fmt.Printf("I'm %d years old.
", old)
}

Output:

I'm 20 years old.

As the documentation for fmt.Println states, this function does not support format specifiers. Use fmt.Printf instead.