Question

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How do I select a range of values in a switch statement?

I’ve been getting some errors, and I’ve been searching for some time now, but I have no idea what is the cause of the errors. (I’m quite new to programming.)

Here are the errors I’m getting:

error: 'Essais' cannot appear in a constant-expression| (line 200)
warning: overflow in implicit constant conversion| (line 202)

I have case and cote:

  char AfficherCote (int Essais)
 {
 char Cote;
 switch (Essais)
  {
(line200)       case Essais<=20:
    {
(line 202)           Cote='Excellent';

        return (Cote);
        break;
    }
    case Essais<=40:
    {
        Cote='Très bon';
        return (Cote);
        break;
    }
    case Essais<=60:
    {
        Cote='Bon';
        return (Cote);
        break;
    }
    case Essais<=80:
    {
        Cote='Moyen';
        return (Cote);
        break;
    }
    case Essais<=100:
    {
        Cote='Muvais';
        return (Cote);
        break;
    }
    case Essais>=100:
    {
        Cote='Très mauvais';
        return (Cote);
    }
  }
}

Answer 1

switch-case only works with constant values^(*) (such as 3 or 'a'), not with ranges (such as <=100). You also must not include the variable name in the case statement. Correct syntax would be as follows:

switch (Essais)
{
case 1:
   /* ... */
  break;
case 2:
   /* ... */
   break;
default:
   /* ... */
}

If you need range tests, use if instead of switch-case:

if (Essais <= 80)
  return "Cote";
else if (Essais <= 100)
  return "Muvais";

Also note that you can’t use single quotation marks ' for strings. Use double quotation marks " instead, and use variables of type std::string (not char) to store strings.

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^(*) To be precise, the condition given in the case statements must be a constant expression of integral type, enumeration type, or class type convertible to integer or enumeration type (see §6.4.2/2 of the C++ Standard for details).