I’m new with Golang and I’ve started to read the book by A. Donovan, and I have a question in the end of one of chapters. He describes type declarations and type’s methods.
And I don’t understand why I get different results with the same call function Printf and Println?

So, we have the example

type Celsius float64
func (c Celsius) String() string { return fmt.Sprintf("%g°C", c) }
c := FToC(212.0)

and have different calls functions of fmt package

fmt.Println(c.String()) // "100°C"
fmt.Printf("%v\n", c) // "100°C"; no need to call String explicitly
fmt.Printf("%s\n", c) // "100°C"
fmt.Println(c) // "100°C"
fmt.Printf("%g\n", c) // "100"; does not call String
fmt.Println(float64(c)) // "100"; does not call String]]

The function FToC converts temperature from two scales if it’s matter.

Printf and Println have different operands in both cases, but I’m not sure this is the answer. I have read about Stringer interface, but, as I understand, the entire package fmt looks for the method from this interface and prints values according to instructions from that. Then why does one method from fmt call String and another method don’t?