Sounds like homework. Show the full assignment and/or the code you have so far.

Right now your question is way to generic.

Yeah, I am starting to get in over my head here.

All right, that's a good start.

Let me just give a couple of examples that are all slightly different to give you some insight into different methods.

Remember that the mouseOver is based on the current size of the rect (as w and h change), not the original size.

Example 1: mouseOver toggles between two sizes

1. int x = 50;
2. int y = 50;
3. int w = 100;
4. int h = 75;
5. 
   
6. void setup() {
7.   size(500, 500);
8. }
9. 
   
10. void draw() {
11.   if (mouseX > x && mouseX < x + w && mouseY > y && mouseY < y + h) {
12.     w = 200;
13.     h = 155;
14.   } else {
15.     w = 100;
16.     h = 75;
17.   }
18. 
    
19.   background(0);
20.   fill(175);
21.   rect(x, y, w, h);
22. }

Example 2: mouseOver makes size grow/shrink (no maximum size)

1. int x = 50;
2. int y = 50;
3. int w = 100;
4. int h = 75;
5.  
6. void setup() {
7.   size(500, 500);
8. }
9.  
10. void draw() {
11.   if (mouseX > x && mouseX < x + w && mouseY > y && mouseY < y + h) {
12.     w = w + 10;
13.     h = h + 10;
14.   } else {
15.     if (w > 100) { w = w - 10; }
16.     if (h > 75) { h = h - 10; }
17.   }
18.  
19.   background(0);
20.   fill(175);
21.   rect(x, y, w, h);
22. }

Example 3: mouseOver makes size grow/shrink between a maximum and minimum size

1. int x = 50;
2. int y = 50;
3. int w = 100;
4. int h = 75;
5. int maxW = 300;
6. int maxH = 200;
7.  
8. void setup() {
9.   size(500, 500);
10. }
11.  
12. void draw() {
13.   if (mouseX > x && mouseX < x + w && mouseY > y && mouseY < y + h) {
14.     if (w < maxW) { w = w + 10; }
15.     if (h < maxH) { h = h + 10; }
16.   } else {
17.     if (w > 100) { w = w - 10; }
18.     if (h > 75) { h = h - 10; }
19.   }
20.  
21.   background(0);
22.   fill(175);
23.   rect(x, y, w, h);
24. }

Example 4: mousePressed toggles a boolean that makes the shape grow/shrink between a max & min size

1. int x = 50;
2. int y = 50;
3. int w = 100;
4. int h = 75;
5. int maxW = 300;
6. int maxH = 200;
7. boolean growing = false;
8.  
9. void setup() {
10.   size(500, 500);
11. }
12.  
13. void draw() {
14.   if (growing == true) {
15.     if (w < maxW) { w = w + 10; }
16.     if (h < maxH) { h = h + 10; }
17.   } else {
18.     if (w > 100) { w = w - 10; }
19.     if (h > 75) { h = h - 10; }
20.   }
21.  
22.   background(0);
23.   fill(175);
24.   rect(x, y, w, h);
25. }
26.  
27. void mousePressed() {
28.   if (mouseX > x && mouseX < x + w && mouseY > y && mouseY < y + h) {
29.     growing = !growing;
30.   }
31. }

With regard to the mouseOver check. Usually they are written including "equal to", like so: mouseX >= x

Another unrelated tip with regard to adding, subtracting, multiplying etc.

There are ways to shorten your code. For example here are three ways to write add 1 to x:

1. x = x + 1;
   
2. x += 1; // also works for - * /
   
3. x++; // this is an even shorter way for adding (or substracting: x--) 1
   

These ways of writing will save you typing and make your code more concise.

thank you very much for this. I like the way you do you coding, it is really easy to read.