Array help- creating new objects that move on a rectangular path

Programming Questions

nr_theyre..

Array help- creating new objects that move on a rectangular path

in Programming Questions • 2 years ago

I'm pretty new at using arrays, so bear with me... what I'm trying to do is make a railroad track situation, where every time the mouse is pressed it adds 2 new "trains" to the line of them. I only have 4 down at the moment, and something tells me this could be done with much less code than what I'm doing so far. Any help with the concept would be really appreciated.

Here's what I have (instantly recognizable problems: only the first one moves, and trainCount never goes above 4)

float[] trainX = {100, 150, 200, 250, 300, 350, 400, 450};
float[] trainY = {100, 100, 100, 100, 100, 100, 100, 100};
int trainCount;
int i = trainCount;
boolean movetrain1, movetrain2, movetrain3, movetrain4;

void setup(){
size(640, 580);
}

void draw(){
println("trainCount = " + trainCount);
background(20);
    trainCount = 2;
    if(mousePressed){
      trainCount += 2;
    }

if((trainX[i] <= 100) && (trainY[i] <= 100)){
    movetrain1 = true;
    movetrain2 = false;
    movetrain3 = false;
    movetrain4 = false;
}else if((trainX[i] >= 500) && (trainY[i] <= 100)){
    movetrain1 = false;
    movetrain2 = true;
    movetrain3 = false;
    movetrain4 = false;
}else if((trainX[i] >= 500) && (trainY[i] >= 500)){
    movetrain1 = false;
    movetrain2 = false;
    movetrain3 = true;
    movetrain4 = false;
}else if((trainX[i] <= 100) && (trainY[i] >= 500)){
    movetrain1 = false;
    movetrain2 = false;
    movetrain3 = false;
    movetrain4 = true;
}

if(movetrain1 == true){
    moveTrain1();
}else if(movetrain2 == true){
    moveTrain2();
}else if(movetrain3 == true){
    moveTrain3();
}else if(movetrain4 == true){
    moveTrain4();
}

if(trainCount >= 1){
    rect(trainX[0], trainY[0], 45, 45);
}
if(trainCount >= 2){
    rect(trainX[1], trainY[1], 45, 45);
}
if(trainCount >= 3){
    rect(trainX[2], trainY[2], 45, 45);
}
if(trainCount >= 4){
    rect(trainX[3], trainY[3], 45, 45);
}

}

void moveTrain1(){
trainX[i]++; //Need to move every member of the array, i think. Want to be able to modify/use all values of trainX and trainY at the same time
}
void moveTrain2(){
trainY[i]++;
}
void moveTrain3(){
trainX[i]--;
}
void moveTrain4(){
trainY[i]--;
}

Replies(4)

torfuspol..

Re: Array help- creating new objects that move on a rectangular path

2 years ago

I can spot several things that are either wrong or that I don't understand. I'll just go through them one at a time

Number 1: Do you want an upper limit for the number of trains or not? Arrays are wonderful if you know the number of objects/variables beforehand (say, 10 trains), but if you want to keep things very flexible, lists are often a better choice. Unfortunately, lists are a bit more complex than arrays.

Number 2: A good sign that you should probably use an array is if your code contains several variables that do almost the same thing, but for slightly different targets. For example, you have variables movetrain1, movetrain2, movetrain3, and movetrain4. We will see later on why using an array, like boolean[] moveTrain, is the better option here.

Number 3: The whole purpose of arrays is that you can use loops for performing the same operation on every element of the array. For example, in your draw method, you got the following code:

if(movetrain1 == true){
moveTrain1();
}else if(movetrain2 == true){
moveTrain2();
}else if(movetrain3 == true){
moveTrain3();
}else if(movetrain4 == true){
moveTrain4();
}

This might by OK for 4 trains, but what if you later decide that you want to have 100 trains? When you use an array, you can do it like this:

for (int j = 0; j < moveTrain.length; j++) {
if (moveTrain[j]) {
moveTrain(j);
}
}

Notice that this code doesn't depend on the total number of trains, because it uses the length property of the array to check how many items the array contains. Now what you still need is a single moveTrain method that allows you to move any train you want (instead of the individual methods for each train like in your code):

public void moveTrain(int trainNumber) {
if (trainX[trainNumber] <= 110 & trainY[trainNumber] == 10) {
trainX[trainNumber] += 1;
} else if (trainX[trainNumber] == 110 & trainY[trainNumber] <= 110) {
trainY[trainNumber] += 1;
} else if (trainX[trainNumber] >= 10 & trainY[trainNumber] == 110) {
trainX[trainNumber] -= 1;
} else {
trainY[trainNumber] -= 1;
}
}

As you can see, this method will move the train whose number is passed using the trainNumber parameter. So if you call moveTrain(1), then the first train is moved, whereas moveTrain(3) moves the third train. This code runs the trains on a square from (10, 10) to (10, 110) to (110, 110) to (10, 110) and back to (10, 10). Of course you can change that to anything you like.

Number 4: I don't really understand what you're trying to do with this snippet of code:

trainCount = 2;
if(mousePressed){
trainCount += 2;
}

You're first setting trainCount to 2, and then add 2 to it if the mouse is pressed. Why?

I hope this answers at least some of your questions. I suggest you try again to make your code do what you want using the hints I gave you (that way you'll understand it better than if I simply gave you a finished piece of code). Feel free to ask more questions if something isn't clear!

nr_theyre..

Re: Re: Array help- creating new objects that move on a rectangular path

2 years ago

Hmm. Well the trainCount being declared in draw() was an obvious flaw, thanks.

Being a noob who has mostly only worked with individual functions so far, this is still pretty confusing... though this definitely puts me in the right direction.

I see I might have made the code confusing by having only 4 trains and also having 4 moveTrain functions - the 4 moveTrain functions were for making them change direction along their rectangular path; right, then down, then left, then up. I assume you bypassed all of that and put them all into one function. So you used trainNumber as each member of the array, and int j to equal it?

I think this is closer, but I'm not completely sure:

float[] trainX = {100, 150, 200, 250, 300, 350, 400, 450};
float[] trainY = {100, 100, 100, 100, 100, 100, 100, 100};
int trainNumber, trainCount;
int j = trainNumber;
int i = trainCount;

void setup(){
size(640, 580);
background(20);
trainCount = 2;
}

public void moveTrain(trainNumber) {
if (trainX[trainNumber] <= 110 & trainY[trainNumber] == 10) {
    trainX[trainNumber] += 1;
} else if (trainX[trainNumber] == 110 & trainY[trainNumber] <= 110) {
    trainY[trainNumber] += 1;
} else if (trainX[trainNumber] >= 10 & trainY[trainNumber] == 110) {
    trainX[trainNumber] -= 1;
} else {
    trainY[trainNumber] -= 1;
}
}

void draw(){
println("trainCount = " + trainCount);

if(mousePressed){
    trainCount += 2;
}

if(trainCount >= 1){
    rect(trainX[0], trainY[0], 45, 45);
}
if(trainCount >= 2){
    rect(trainX[1], trainY[1], 45, 45);
}
if(trainCount >= 3){
    rect(trainX[2], trainY[2], 45, 45);
}
if(trainCount >= 4){
    rect(trainX[3], trainY[3], 45, 45);
}
if(trainCount >= 5){
    rect(trainX[4], trainY[4], 45, 45);
}
if(trainCount >= 6){
    rect(trainX[5], trainY[5], 45, 45);
}

for (int j = 0; j < moveTrain.length; j++) {
if (moveTrain[j]) {
      moveTrain(j);
    }
}
}

Thanks so much

torfuspol..

Re: Array help- creating new objects that move on a rectangular path

2 years ago

Okay, I think it might be easier if we make the problem a bit more simple before continuing. Note that that's always a good idea, because it's much easier to make a simple program more complicated instead of the other way round

So instead of going around a rectangular path, let's just say each train moves from x = 10 to x = 110 on its own railway. If you have one train, you can do it like this:

int trainPos = 10;
void draw() {
background(255);
if (trainPos < 110) {
trainPos++;
}
ellipse(trainPos - 5, 5, 10, 10);
}

If you add another train, which starts a little bit ahead, you're code might look like this:

int trainPos1 = 10;
int trainPos2 = 30;
void draw() {
background(255);
if (trainPos1 < 110) {
trainPos1++;
}
if (trainPos2 < 110) {
trainPos2++;
}
ellipse(trainPos1 - 5, 5, 10, 10);
ellipse(trainPos2 - 5, 5, 10, 10);
}

Now there are three indicators that you should probably use arrays:

Two variables named trainPos1 and trainPos2
Two very similar looking parts for moving the trains
Two very similar looking lines for drawing the trains

Of course it's not such a problem with just two trains, but again think about having 100 trains.

To convert the code to arrays, you need to do two things:

Collect all suitable variables in arrays
Replace repeated code with loops

In our example, step 1 means using an array for storing the train positions:

int[] trainPos = {10, 50};
void draw() {
background(255);
if (trainPos[0] < 110) {
trainPos[0]++;
}
if (trainPos[1] < 110) {
trainPos[1]++;
}
ellipse(trainPos[0] - 5, 5, 10, 10);
ellipse(trainPos[1] - 5, 5, 10, 10);
}

The important thing to note here is that array indices start at 0, so the first train's position is trainPos[0].

Now the second step means we need to create a loop for moving the trains and one for drawing them. Since our example is so short, there's no problem of using a single loop to do both at once:

int[] trainPos = {10, 50};
void draw() {
background(255);
for (int i = 0; i < trainPos.length; i++) {
if (trainPos[i] < 110) {
trainPos[i]++;
}
ellipse(trainPos[i] - 5, 5, 10, 10);
}
}

Note that now the only code which depends on the actual number of trains is the first line, since the loop uses the length property of the array to get the number of trains. So by simply replacing the first line with

int[] trainPos = {10, 50, 80};

you get 3 trains instead of 2.

As an exercise, you can try to give each train a different size (stored in a new array), and then use this size in the drawing loop.

nr_theyre..

Re: Re: Array help- creating new objects that move on a rectangular path

2 years ago

Alright. I think I'm a lot closer. Maybe fooling around more with booleans and functions could help...but it seems like I tried everything :/

This almost works (halfway around the path messes up):

int[] trainPosX = {10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240};
int[] trainPosY = {10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240};
int trainCount;

boolean x250, y250;

void setup(){
size(400, 400);
trainCount = 1;
}

void draw() {
background(255);
for (int i = 0; i < trainPosX.length; i++) {
    if(trainPosX[i] == 250){
      x250 = true;
    }else{
      x250 = false;
    }
    if(trainPosY[i] == 250){
      y250 = true;
    }else{
      y250 = false;
    }

    if((x250 == false) && (y250 == false)){
    trainPosX[i]+=2;
    trainPosY[i] = trainPosY[00];
    }
    else if((x250 == true) && (y250 == false)){
    trainPosX[i] = trainPosX[i];
    trainPosY[i]+=2;
    }
    else if((x250 == true) && (y250 == true)){
    trainPosX[i]-=2;
    trainPosY[i] = trainPosY[i];
    }
    else if((x250 == false) && (y250 == true)){
    trainPosX[i] = trainPosX[i];
    trainPosY[i]-=2;
    }

if(trainCount >= 1){
    rect(trainPosX[0], trainPosY[0], 10, 10);
}
if(trainCount >= 2){
    rect(trainPosX[1], trainPosY[1], 10, 10);
}
if(trainCount >= 3){
    rect(trainPosX[2], trainPosY[2], 10, 10);
}
if(trainCount >= 4){
    rect(trainPosX[3], trainPosY[3], 10, 10);
}
if(trainCount >= 5){
    rect(trainPosX[4], trainPosY[4], 10, 10);
}
if(trainCount >= 6){
    rect(trainPosX[5], trainPosY[5], 10, 10);
}
if(trainCount >= 7){
    rect(trainPosX[6], trainPosY[6], 10, 10);
}
if(trainCount >= 8){
    rect(trainPosX[7], trainPosY[7], 10, 10);
}
if(trainCount >= 9){
    rect(trainPosX[8], trainPosY[8], 10, 10);
}
if(trainCount >= 10){
    rect(trainPosX[9], trainPosY[9], 10, 10);
}
if(trainCount >= 11){
    rect(trainPosX[10], trainPosY[10], 10, 10);
}

float time = second();
if(time%1 == 0){
trainCount++;
}
}
}

////////////////////////////////////////////////////

And then this one's code seems to be more simplified, but doesn't work as well:

float[] trainX = new float[36];
float[] trainY = new float[36];
int trainCount;

void setup(){
size(800, 600);
trainCount = 1;
}

void draw(){
background(0);
for(int i = 0; i < trainX.length; i++){
if((trainX[i] <= 251) && (trainY[i] <= 140)){
    trainX[i]+=5;
    trainY[i] = trainY[i];
}else if((trainX[i] >= 700) && (trainY[i] <= 140)){
    trainX[i] = trainX[i];
    trainY[i]+=5;
}else if((trainX[i] >= 700) && (trainY[i] >= 590)){
    trainX[i]-=5;
    trainY[i] = trainY[i];
}else if((trainX[i] <= 251) && (trainY[i] >= 590)){
    trainX[i] = trainX[i];
    trainY[i]-=5;
}
rect(trainX[trainCount-1], trainY[trainCount-1], 50, 50);
println("trainCount: " + trainCount);
}
if(mousePressed){
    trainCount++;
}
}