无法创建switch语句

Question

I am very new to C++, and I am having trouble completing an assignment. I need to switch this if statement to a switch statement, but I am totally lost on how to do it since the number must be an integer. Could someone point me in the right direction?

See below:

#include <iostream>
#include <iomanip>
using namespace std;

int main()
{
  //declare named constants and variables
  const double RATE1 = .02;
  const double RATE2 = .05;
  double sales       = 0.0;
  double commission  = 0.0;

  //get input item
  cout << "Enter the sales amount: "; 
  cin >> sales; 

  //calculate commission
  if (sales <= 15000.0)
{
    commission = sales * RATE1;
else
    commission = sales * RATE2;

 }
//end if

//display commission
  cout << fixed << setprecision(2);
  cout << "Commission: $" << commission << endl;

system("pause");
return 0;
}   //end of main function

Answer 1

This is not feasibly possible to do. switch requires integral equality, your code checks for lesser than on a double number.

The unfeasible option would be to convert your double to integer with lost precision and than list all 15000 options as case labels. Not feasible at all.

Answer 2

If you use gcc then you can use case ranges: Case Ranges , but this works IMHO for integral data types, I am not sure about doubles.

But don't forget, this is only the extension of the compiler. I also heard something similar was introduced with C++11, but I am not sure there.

Answer 3

You can technically do it in this horrible way:

//calculate commission
switch (sales <= 15000.0)
{
case true: 
    commission = sales * RATE1;
    break;
default:
    commission = sales * RATE2;
}

But never, ever do this in real code.

Answer 4

As SergeyA pointed out in his answer this is feasible as it is a huge range of cases.

If it absolutely needs to have a switch statement then we can cheat and have a function that returns true or false and then switch on the result of that function

bool is_less(double amount)
{
    return amount < 15000.0;
}

//...

switch (is_less(sales))
{
    case true: commission = sales * RATE1; break;
    case false: commission = sales * RATE2; break;
}

Answer 5

You could do something like this, similar to NathanOliver's answer without a new function.

#include <iostream>
#include <iomanip>
using namespace std;

int main()
{
  //declare named constants and variables
  const double RATE1 = .02;
  const double RATE2 = .05;
  double sales       = 0.0;
  double commission  = 0.0;

  //get input item
  cout << "Enter the sales amount: "; 
  cin >> sales; 

  //calculate commission

  bool lessthan = sales <= 15000.0;

  switch (lessthan) 
  {
      case true: 
          commission = sales * RATE1;
          break;

      case false: 
        commission = sales * RATE2;
        break;

      default: 
        break;        
  }

//display commission
  cout << fixed << setprecision(2);
  cout << "Commission: $" << commission << endl;

  system("pause");
  return 0;
}   //end of main function`