Simple Calculator with Go

calc.go

package main

import "fmt"

const (
  O_NOTHING float32 = iota
  O_ADD float32 = iota
  O_SUBSTRACT float32 = iota
  O_MULTIPLY float32 = iota 
  O_DIVIDE float32 = iota
)

const CONFIRM_MSG = "Continue calculation with existing data";

func main() {
 var initial_value float32 = 0;
 calc(&initial_value, false);
}

func calc(previous *float32, continue_calc bool) {
  var result, operation_ptr = calc_start(previous, continue_calc);

  if (*operation_ptr == O_NOTHING) {
   fmt.Println("Nothing selected, aborting...");
   return;
  }

  fmt.Printf("Result: %f\n", result);

  var confirm bool = confirm(CONFIRM_MSG);

  if (confirm) {
    *previous = result;
    calc(previous, true)
  }
}


func calc_request_operation() float32 {
  fmt.Println("AVAILABLE OPERATIONS: \n 1: Addition (+)\n 2: Substraction (-)\n 3: Multiply (*)\n 4: Divide (*)\n\n");

  fmt.Print("Select operation [0-3]: ");
  var a float32;
  fmt.Scanf("%f", &a);
  return a;
}

func confirm(text string) bool {
  fmt.Printf("%s [y/n]?: ", text);
  var confirm string;
  fmt.Scanf("%s", &confirm);

  return (confirm == "y");
}

func calc_prompt(num int) float32 {
  fmt.Print("Enter a number ", num, ": ");
  var a float32;
  fmt.Scanf("%f", &a);
  return a;
}

func calc_start(start_value *float32, continue_calc bool) (float32, *float32) {
  var x float32;

  if (continue_calc) {
    x = *start_value;
  } else {
    x = calc_prompt(1);
  }

  var y float32 = calc_prompt(2);

  var operation float32 = calc_request_operation();
  var result float32;

  switch operation {
  case O_ADD:
    result = x + y;
    break;
  case O_SUBSTRACT:
    result = x - y;
    break;
  case O_MULTIPLY:
    result = x * y;
    break;
  case O_DIVIDE:
    result = x / y;
    break;
  default:
    fmt.Println("** ERROR **: Unknown operation: ", operation);
    operation = O_NOTHING;
    result = 0;
  }

  return result, &operation;
}

func obj_exp() {
  var x human = human{"Ivan", 32}
  var y human = human{"Iva" + "n", 31 + 1}
  fmt.Println("Object equals? - ", x == y)
  fmt.Println("Addresses equals? - ", &x == &y)
}