Multi-Color Rectangles

My goal is to create Multi-color rectangles that gets bigger when "Left-Clicked" and smaller when "Right-Clicked". I also want to add a keyboard press that changes its color when pressed.

The problem with my code are:

1. "Out of bounds exceptions" - How can I possibly fix this? If it reaches the end of the index, I would like it to stay at the last index and not throw an out of bounds error

2. Rectangles keeps changing its color when "keyPressed()" is called inside the "draw()".

When I call the "keyPressed()" inside the "setup()", I losses the mousePressed() function.

How could I incorporate these two function having static rectangles that only changes the color when Keyboard is pressed and gets bigger or smaller when the mouse button is pressed?

int[] numberOfChoices = {5, 10, 20, 25, 50, 100, 125, 250}; //an array that defines the sizes of rectangles
int arrayNum;
void setup(){
  size(500,500);
  
}

void draw(){
 
  keyPressed();
 
}

void keyPressed(){
  for(int x = 0; x < width; x+=numberOfChoices[arrayNum]){
    for(int y = 0; y < height; y+=numberOfChoices[arrayNum]){
      fill(random(255), random(255), random(255));
      rect(x,y,numberOfChoices[arrayNum],numberOfChoices[arrayNum]);
    }
  }
}  

void mousePressed(){
if(mouseButton==LEFT){
 arrayNum +=1;
}
else arrayNum-=1;

}

Use the % remainder operator to have arrayNum stay within the boundaries. For this to work, you need to replace add length when subtracting one.

void mousePressed() {
    if (mouseButton == LEFT) {
        arrayNum = (arrayNum + 1) % numberOfChoices.length;
    } else {
        arrayNum = (arrayNum + numberOfChoices.length - 1) % numberOfChoices.length;
    }
}

You can combine this using ternary conditional operator:

void mousePressed() {
    arrayNum = (arrayNum + (mouseButton == LEFT ? 1 : numberOfChoices.length - 1)) % numberOfChoices.length;
}

If you don't like the use of the remainder operator, you can always just do it with if statements:

void mousePressed() {
    if (mouseButton == LEFT) {
        arrayNum++;
        if (arrayNum >= numberOfChoices.length)
            arrayNum = 0; // roll over to first choice
    } else {
        arrayNum--;
        if (arrayNum < 0)
            arrayNum = numberOfChoices.length - 1; // roll over to last choice
    }
}

Or if you don't want rollovers:

void mousePressed() {
    if (mouseButton == LEFT) {
        // Increment if before last choice
        if (arrayNum < numberOfChoices.length - 1)
            arrayNum++;
    } else {
        // Decrement if after first choice
        if (arrayNum > 0)
            arrayNum--;
    }
}