switch/case in C

[Rap]

Hallo,

Ich bin C-Anfänger. Im Internet habe ich folgende Switch/Case Anweisung gefunden:
_____________________________________________________________
    char op;
    .
    .
    .
    switch(op)
    {
        case "+":
                        scanf("%f",&operator);
                        erg+=operator;
                        break;
        case "-":
                        scanf("%f",&operator);
                        erg-=operator;
                        break;
        case "*":
                        scanf("%f",&operator);
                        erg*=operator;
                        break;
        case "/":
                        scanf("%f",&operator);
                        if(operator!=0)
                        {
                        erg/=operator;
                        }
                        else
                        {
                        printf("Division durch 0!");}
                        break;
        case "=":
         break;
    }
    .
    .
    .
_____________________________________________________________

Der Compiler meldet bei jeder Case-Anweisung: "case label does not reduce to an integer constant"

Wie kann ich (in C) mit case eine Variable vom Datentyp char abfragen?

MFG

Rap