How to convert the data type correctly?

Question

go

I am new to Golang, learning the second day. I decided to make a simple calculator for practice, but something doesn’t work out very well.

Here is the code for the calculator itself:

package main

import (
  "fmt"
  "os"
)

func main() {

  var what string
  var a float64
  var b float64

  fmt.Print("Выберите действие (+, -)")
  fmt.Fscan(os.Stdin, &what)

  fmt.Print("Введите первое значение: ")
  fmt.Fscan(os.Stdin, &a)

  fmt.Print("Введите второе значение: ")
  fmt.Fscan(os.Stdin, &b)

  var c float64
  if what == "+" {
    c = a + b
    fmt.Println("Результат: " + c)
  } else if what == "-" {
    c = a - b
    fmt.Println("Результат: " + c)
  }
}

Error:
# command-line-arguments
.\calc.go:26:38: cannot use "Result: " (type untyped string) as type float64
.\calc.go:29:38: cannot use "Result: " (type untyped string) as type float64

When I try to convert variable "c" to string, I get another error:
# command-line-arguments
.\calc.go:26:38: cannot use "Result: " (type untyped string) as type float64
.\calc.go:29:38: cannot use "Result: " (type untyped string) as type float64

Answer 1

When you read data from the console, it comes to you as a string.
Those. first you need to read it into a string, and then you need to convert the string to a float.
Here is a working example

package main

import (
    "fmt"
    "log"
    "os"
    "strconv"
)

func main() {

    var what string
    var input string

    fmt.Print("Выберите действие (+, -)")
    fmt.Fscan(os.Stdin, &what)
    if what != `+` && what != `-` {
        log.Fatalf("действие указанно не корректно\n")
    }

    fmt.Print("Введите первое значение: ")
    fmt.Fscan(os.Stdin, &input)
    a, err := strconv.ParseFloat(input, 64)
    if err != nil {
        log.Fatalf("число указано не корректно: %v\n", err)
    }

    fmt.Print("Введите второе значение: ")
    fmt.Fscan(os.Stdin, &input)
    b, err := strconv.ParseFloat(input, 64)
    if err != nil {
        log.Fatalf("число указано не корректно: %v\n", err)
    }

    var c float64
    if what == "+" {
        c = a + b
    } else if what == "-" {
        c = a - b
    }

    fmt.Printf("Результат: %v\n", c)
}

If these are your first steps in programming, it is better to start with Python, it will significantly simplify the start.