How does this code move the bird sprite in this sketch?

Question

I'm teaching this sketch in my class. I understand most of the sketch and can see the class that makes the bird move, but I still don't quite understand how the code makes the sprite "move." I can also see what generates the Pipes but I don't how the code creates them or randomizes them.

Here is the code for both:

Bird

class Chym {
private:
 int frameCount;
 int x; 
 int y;
 int deltaIde;
 int delayFrame;
 int jumpCount; 
 int maxJumpCount;
 int moveSpeed;
 bool _isDead;
public: 
 void respawn() {
 x = 24; 
 y = 20;
 deltaIde = -1;
 moveSpeed = 1;
 jumpCount = 0;
 _isDead = false;
 }
 Chym() {
 frameCount = 0;
 delayFrame = 0;
 maxJumpCount = 20;
 respawn();
 }
 void render() {
 if (frameCount < ANIM_FRAME / 2) {
 display.drawBitmap(x, y, flappybird_frame_1, 16, 12, 1); 
 } 
 else {
 display.drawBitmap(x, y, flappybird_frame_2, 16, 12, 1); 
 }
 }
 void update() {
 delayFrame++;
 if (delayFrame == DELAY_FRAME) {
 y += deltaIde * moveSpeed;
 delayFrame = 0;
 }
 if (y > 35) {
 _isDead = true;
 }
 frameCount++;
 if (frameCount >= ANIM_FRAME) frameCount = 0;
 }
 bool isDead() {
 return _isDead;
 }
 void die() {
 _isDead = true;
 }
 void cancelJump() {
 jumpCount = 0;
 flyDown();
 }
 void flyUp() {
 if (jumpCount < maxJumpCount) {
 deltaIde = -1; 
 moveSpeed = 3; 
 jumpCount++;
 } 
 else {
 flyDown();
 }
 }
 void flyDown() {
 deltaIde = 1; 
 moveSpeed = 1;
 }
 int getX() {
 return x;
 }
 int getY() {
 return y;
 }
}; 

Pipe

class Bar {
private:
 int x; 
 int y;
 int delayFrame;
 int moveSpeed;
public: 
 Bar() {
 delayFrame = 0;
 x = 0; y = 24;
 moveSpeed = 2;
 }
 void setPos(int sx, int sy) {
 x = sx; y = sy;
 }
 void render() {
 display.drawBitmap(x, y - 30, bar_top, 8, 20, 1); 
 display.drawBitmap(x, y + 10, bar_bottom, 8, 20, 1); 
 }
 void update() {
 delayFrame++;
 if (delayFrame == DELAY_FRAME) {
 x -= moveSpeed;
 if (x < -10) x = 95;
 delayFrame = 0;
 }
 }
 int hitTest(int tx, int ty) {
 int hitX = ((tx >= x - 16) && (tx <= x))?1:0;
 int hitY = ((ty <= (y - 10)) || (ty + 12 >= y + 10))?1:0;
 if (hitX != 0) {
 return hitY;
 }
 return 0;
 }
};

https://www.youtube.com/watch?v=04cY78Y2d3g

Answer 1

This part of your code is what changes the sprite's y-value.

y += deltaIde * moveSpeed;

When you click the "jump" button or when the bird falls the y-value is changed to reflect either an upward movement or a downward movement. When your render() method is called the bird will either be drawn higher up on the y-axis (it's flying) or lower on the y-axis (it's falling).

As for the bars, if you watch closely in the video you can see that they aren't actually randomized.

Compound Assignment Operators

+= is the "plus assign" operator. It adds whatever is on the right side to the variable on the left side. Here is a table of other compound assignment operators: https://en.wikipedia.org/wiki/Operators_in_C_and_C%2B%2B#Compound_assignment_operators

int x = 5;
x += 2; // equals 7; equivalent to x = x + 2;
x = 5;
x = x + 2; // also equals 7; equivalent to x += 2;

• Gabe Ruiz: What does the += mean?
• Avamander: @GabeRuiz, it was said in the same post:"x += 2; // equals 7; equivalent to x = x + 2;"
• Gabe Ruiz: @Avamander if you'll notice the post was edited after my comment to include the answer to my second question, but thank you for pointing it out.
• Gabe Ruiz: @Chris, thank you for the link. It has helped a lot.