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The Case Statement

JohnDSiviter

I have wrote the following:

 

  if (PA!=NAPA)
  {
   switch(NAPA)
   {
      case 0x00:
        switch (PA) //check last state
        {
         case 0x02:myvolume++; break;
         case 0x01:myvolume--; break;
        }
       break;

       case 0x01:
        switch (PA)
        {
         case 0x00:myvolume++; break;
         case 0x03:myvolume--; break;
        }
       break;

      case 0x03:
        switch (PA)
        {
         case 0x01:myvolume++; break;
         case 0x02:myvolume--; break;
        }
       break;
         
       case 0x02:
        switch (PA)
        {
         case 0x03: myvolume++; break;   
         case 0x00: myvolume--; break;
        }
       default:break;
   }

  }

 

My question is, is it possible to combine multiple cases somehow, like:

 

case 0x00 OR case 0x01, if I could do something like this I could reduce it further.

 

This is a routine to detect the direction of a greyscale(or Manchester) encoder and change the volume accordingly.

  • hi,

     

    My answer is NO. Case statements should be constant and not conditional. But you can write something a bit more clear,

     

    case 0x00 :

    case 0x01 : do_something(); break;

     

    Firat

  • Firs tof all, consider the constrcution

    switch (c)

         case a:

              <codeA>

         case b:

              <codeAB>

              break;

         case c:

              ...

     

    In your case you have 2 variables to be checked, you can only do this simultaneously in if... then constructions, wich reads al little bit harder than the switch...case cunstruction

     

    Most important is to maintain readablity in your code. Sometimes it's far more convenient to have code that reads like a magazine, than to have very 'smart' written code that nobody else but you understands.

    Another thing to consider is the fact that the compiler plays a very important role in how efficient the code is. Therefore you could look at the assembly language generated by the compiler. Sometimes the 'smart' solution (with fewer lines in C-code) may produce a lot more machine code than you would expect.

     

    Kris

  • John, the best way is to do this mathemagically.  If PS is the previous 2 bit state of your gray code input and CS is the current 2 bit state of the gray code input then:

     

         CS = get 2 bit gray code input; eg 00, 01, 11 or 10

         byte DIR = ((CS >> 1) ^ PS) & 1;

         if (DIR == 1)

              do backward stuff

         else

              do forward stuff

         PS = CS;

     

    You might need to draw a bit map to understand the logic.  This will be orders of magnitude more efficient than a collection of case statements.

  • in reply to Former Member

    Hi thanks for the responses, James: thanks you gave me an idea to reduce the boolean equivalent.