typedef struct
{
  int d0, d1, d2, d3, d4, d5, d6, d7;
  int is_4bits;
} lcd_module;

void lcd_attach(lcd_module* lcd)
{
  if (lcd->is_4bits)
  {
    // Attach 4 bits
  }
  else
  {
    // Attach 8 bits
  }
}

void lcd_send_cmd(lcd_module* lcd, int cmd)
{
  if (lcd->is_4bits)
  {
    // Send 4 bits command
  }
  else
  {
    // Send 8 bits command
  }
}

int main(void)
{
  lcd_module lcd4;
  lcd_module lcd8;

  // Setup
  lcd4.d4 = 1;
  lcd4.is_4bits = 1;

  lcd8.d0 = 2;
  lcd8.is_4bits = 0;
  // Etc

  // Attach
  lcd_attach(&lcd4);
  lcd_attach(&lcd8);
  return 0;
}