switch and case

1. import std.stdio;
   import std.string;
   
   void main() {
       string op;
       double first;
       double second;
   
       write("Please enter the operation: ");
       op = strip(readln());
   
       write("Please enter two values separated by a space: ");
       readf(" %s %s", &first, &second);
   
       double result;
   
       final switch (op) {
   
       case "add":
           result = first + second;
           break;
   
       case "subtract":
           result = first - second;
           break;
   
       case "multiply":
           result = first * second;
           break;
   
       case "divide":
           result = first / second;
           break;
       }
   
       writeln(result);
   }
   

2. By taking advantage of distinct case values:

       final switch (op) {
   
       case "add", "+":
           result = first + second;
           break;
   
       case "subtract", "-":
           result = first - second;
           break;
   
       case "multiply", "*":
           result = first * second;
           break;
   
       case "divide", "/":
           result = first / second;
           break;
       }
   

3. Since the default section is needed to throw the exception from, it cannot be a final switch statement anymore. Here are the parts of the program that are modified:

   // ...
   
       switch (op) {
   
       // ...
   
       default:
           throw new Exception("Invalid operation: " ~ op);
       }
   
   // ...