How to switch program in arduino using android app?
Once I made a sketch to run multiple programs. I wrote a setup and loop function for every different "program", (e.g. setup_p1, setup_p2, ... loop_p1, ...) and then wrote a simple main sketch to handle them all.

In my application I choose the program at startup with a 3-dipswitch, but you can easily switch this to allow "on the fly" switching.

I choose to use a callback because it's faster than just checking the mode every time, at least in my case

// callback for loop function
typedef void (*loopfunction)();
loopfunction currentloop;

void setup()
{
  // Set dip-switch pins as input
  pinMode(MODE_PIN2,INPUT_PULLUP);
  pinMode(MODE_PIN1,INPUT_PULLUP);
  pinMode(MODE_PIN0,INPUT_PULLUP);

  // Concatenate the dip-switch values
  byte mode = 7 - ((digitalRead(MODE_PIN2) &lt;&lt; 2) | (digitalRead(MODE_PIN1) &lt;&lt; 1) | digitalRead(MODE_PIN0));

  // choose the correct mode
  switch(mode)
  {
    case 0: // Shutdown - do nothing
            break;
    case 1: // Program 1
            setup_p1();
            currentloop = loop_p1;
            break;
    case 2: // Program 2
            setup_p2();
            currentloop = loop_p2;
            break;
    ...
  }

  // Not a valid program: halt
  if (!currentloop)
  {
    while(1);
  }
}

void loop()
{
  // Execute the current loop
  currentloop();
}