Calculating delta time

Projects Programming
5

Here's my entire code. Ok I understand that maybe I should keep the time variables as unsigned longs, but why is it that I can't apply my deltaTime to my player character unless I keep everything floats? Is there something going wrong in the conversion?

#include <Arduboy.h>
Arduboy arduboy;

const unsigned char background[] PROGMEM = {0x81, 0x00, 0x12, 0x40, 0x4, 0x11, 0x00, 0x4,};
const unsigned char player[] PROGMEM = {0x00, 0x00, 0x00, 0x00, 0x34, 0xfc, 0x8f, 0x34, 0x6, 0x36, 0x8e, 0x94, 0x60, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x2, 0x1e, 0xe6, 0xa3, 0xda, 0x83, 0xc4, 0xb8, 0x00, 0x00, 0x00, 0x00,};

bool aBuffer;
bool showBG;
float playerX;
float playerY;
float oldTime = 0;

void setup() {
  arduboy.begin();
  arduboy.clear();
  ResetGame();
}

void loop() {
  float deltaTime = CalculateDeltaTime();
  arduboy.clear();

  // Draw Background.
  if (showBG) {
    for (int i = 0; i < 128; i += 8) {
      for (int j = 0; j < 64; j += 8) {
        arduboy.drawBitmap(i, j, background, 8, 8, WHITE);
      }
    }
  }
  
  // Draw player character.
  arduboy.fillRect(playerX + 4, playerY, 8, 16, BLACK);
  arduboy.drawBitmap(playerX, playerY, player, 16, 16, WHITE);

  if (arduboy.pressed(LEFT_BUTTON))
    playerX -= deltaTime / 4;
  if (arduboy.pressed(RIGHT_BUTTON))
    playerX += deltaTime / 4;
  if (arduboy.pressed(UP_BUTTON))
    playerY -= deltaTime / 4;
  if (arduboy.pressed(DOWN_BUTTON))
    playerY += deltaTime / 4;
  if (arduboy.pressed(A_BUTTON) and !aBuffer) {
    showBG = !showBG;
    aBuffer = true;
  }
  if (arduboy.pressed(A_BUTTON) and arduboy.pressed(B_BUTTON))
    ResetGame();
  if (arduboy.notPressed(A_BUTTON))
    aBuffer = false;
  
  arduboy.display();
}

void ResetGame()
{
  aBuffer = false;
  showBG = true;
  playerX = 5;
  playerY = 10;
  return;
}

float CalculateDeltaTime(){
  float currentTime = millis();
  float deltaTime = currentTime - oldTime;
  oldTime = currentTime;
  return deltaTime;
}