void setup() {
  // Set up the direction register and output register pointers
  volatile char *dir, *dirk, *ink, *outf;
  
  dir = (volatile char *) 0x30;   // Data direction register for output (7-segment)
  dirk = (volatile char *) 0x107; // Data direction register for switch
  ink = (volatile char *) 0x106;  // Input register (switch input)
  outf = (volatile char *) 0x31;  // Output register for 7-segment display
  
  *dir = 0xFF;   // Set the 7-segment display port as output
  *dirk = 0x00;  // Set the switch port as input
}

void loop() {
  volatile char *ink = (volatile char *) 0x106;  // Input register (switch input)
  volatile char *outf = (volatile char *) 0x31;  // Output register (7-segment display)
  
  // Array holding the 7-segment values for numbers 0 to 9
  char segmentMap[10] = {
    0x3F, // 0
    0x06, // 1
    0x5B, // 2
    0x4F, // 3
    0x66, // 4
    0x6D, // 5
    0x7D, // 6
    0x07, // 7
    0x7F, // 8
    0x6F  // 9
  };

  for (int i = 0; i < 10; i++) {  // Traverse numbers 0 to 9
    *outf = segmentMap[i];         // Set the 7-segment display to show the digit
    
    // Large delay to observe the change
    for (long n = 0; n < 5000000; n++);
  }
}