Switch case questions

Projects Programming
1

Hi all. I am wondering if you can use a switch case with multiple variables. IE

switch (button,switch) {

case (12,LOW):
lcd.print("1"); button=0; //print then clear button to 0
break;

case (10,HIGH):
lcd.print("2"); button=0; //print then clear button to 0
break;

default:
// hop up and down because there is nothing here to do
break;

The idea is that I have a keypad that is writing a value that corresponds to the button that was pushed and a switch that is either on or off. They are both written into the variables button and switch. Is this possible or am I constrained to if/else statements

if (button==12 && switch==HIGH)
{//do forward gymnastics here}
if (button==10 && switch ==LOW)
{//do reverse gymnastics here}

pretty sure that my example syntax is wrong but you get the idea of what I am attempting

Thanks for looking
amachinetech

2

No.

3

with a little math you could

 switch ((button * 10)  + (switch == HIGH) ? 1:0) {

  case (120):
   lcd.print("1"); button=0; //print then clear button to 0
    break;

  case (101):
   lcd.print("2"); button=0; //print then clear button to 0
    break;

  default: 
    // hop up and down because there is nothing here to do
  break;
4

As zhomeslice demonstrates, you can use a computed value.

However, the entire point of a switch statement is that ideally the compiler can crunch it down to a jump table. So it's best if your values are tightly packed rather than sparse, rather than spaced 10 values apart.

5

So the short answer is yes you can do it but it takes work around kung fu to "make it work". So it is simpler to use the if/else and save the switch/case for another day.
Thanks for looking all

amachinetech

6

You might want to give a slightly more real-life example so it's a little clearer what you need to achieve but an array of function pointers comes to mind (maybe in combination with a struct).

The below uses a struct with two elements; the first one is the buttonvalue (number) and the second one is a pointer to a function that needs to be executed. Written to give you an idea what can be done

First you can define the struct

struct BUTTONACTION
{
  byte number;
  void (*action)(byte switchstate);
};

The action is a pointer to a function that takes the 'switchstate' as a parameter

Next you need to write the functions.

void button12(byte switchstate)
{
  if(switchstate == HIGH)
  {
    lcd.print("1");
  }
}

void button10(byte switchstate)
{
  if(switchstate == LOW)
  {
    lcd.print("2");
  }
}

Now you can populate an array of structs with buttons and associated functions

BUTTONACTION buttonactions[] =
{
  {12, button12},
  {10, button10},
  {11, NULL},
};

For button value 11, there is no function specified so nothing will be executed; just to show how it can be used.

setup() will be your standard setup
and loop() can look like below

  byte buttonval = readKeypad();
  byte switchstate = digitalRead(A0);

  // loop through the possible buttons
  for(int cnt=0;cnt<sizeof(buttonactions)/sizeof(buttonactions[0]);cnt++)
  {
    // if the entered button number matches the nunber in the action table
    if(buttonval == buttonactions[cnt].number)
    {
      // and if there is a function specified
      if(buttonactions[cnt].action != NULL)
      {
        // execute the function
        buttonactions[cnt].action(switchstate);
      }

      // optionally break from for-loop after match
      break;
    }
  }

  // reset the enter button number
  buttonval = 0;
}

You can finetune to your needs :wink:

Total

// variable declarations and defines
...
...

struct BUTTONACTION
{
  ...
  ...
};

// button actions
void button12(byte switchval)
{
  ...
  ...
}

...
...

void setup()
{
  ...
  ...
}

void loop()
{
  ...
  ...
}