CS 100 Spring 2014 Lab 3

More Loops

---

Using the Processing language/environment answer the following four questions.

1. [4 pts] Consider the following program that uses a while loop to print increasing numbers on the console and then do the same thing with a for.

println("counting up with a while loop");
int MAX = 5;   // constant declaration used to terminate the loop 
int i = 1;     // initialization of counter variable 
// i is the loop variable, incremented each time through the loop 

while (i <= MAX) { // continutation test: boolean expression
                   // tested before continuing next iteration

  // print the counter followed by a space (no new line)
  print(i + " ");  
  //counter i is updated
  i = i+1;
}
// change line with println
println("");
println("done: out of the while loop");

println("---------------------------");

println("counting up with a for loop");

//Notice that the data type int is not in front of the variable i here
//because i was declared above 
for(i=1; i<=MAX; i=i+1) {
  print(i + " ");
}
println("");
println("done: out of the for loop");

The synthax for a while loop is the following

initialization
while (continuation test) {
   statements
   one statement updates the variable tested in the contintation test
}

where as the syntax of a for loop is

for (initialization; continuation test; update) {
   statements
}

Now that you understand for and while loops, copy the above code into a Processing program called loops and do the following.

• Run the program and examine its output on the console.
• Change one line of the program to print from 1 to 10.
• Declare and use a variable to print starting at 3 for both the while and for loops.
• Add two loops, one while loop and one for loop, below the provided code, such that each counts down from 12 to 0.

The output of loops should be the following

counting up with a while loop
3 4 5 6 7 8 9 10 
done: out of the while loop
---------------------------
counting up with a for loop
3 4 5 6 7 8 9 10 
done: out of the for loop
---------------------------
---------------------------
counting down with a while loop
12 11 10 9 8 7 6 5 4 3 2 1 0 
done: out of the while loop
---------------------------
counting down with for loop
12 11 10 9 8 7 6 5 4 3 2 1 0 
done: out of the for loop

2. [4 pts] Using for or while, whichever you prefer, write a program moreLoops that produces on the console the output below for Loop 1 and Loop 2. Write your code first on a piece of paper, checking manually the loop iterations. (Loop 3 and Loop 4 are bonuses, do them if you have time.)

Loop 1 
0 3 6 9 12 15 18 

Loop 2
20 15 10 5 0 

Extra Loop 3 (power of two)
1 2 4 8 16 32 64 

Extra Loop 4 (sum of i [starts at 1 and stops after 10 iterations])
0 1 3 6 10 15 21 28 36 45

3. [4 pts] Copy the following code into a program called manyEllipses and run it.

size(400, 400);

background(255);
smooth();
fill(random(128, 255), random(128, 255), random(128, 255));
ellipse(random(width), random(height), 50, 50);

fill(random(128, 255), random(128, 255), random(128, 255));
ellipse(random(width), random(height), 50, 50);

Add a loop to create many ellipses, the result is an image like the one below.

4. [4 pts] Write a program called dice that creates a 300 x 300 window and initializes the variables

int dotSize = 25;
int dotX = 40;
int dotY = 40;
int incX = 50;
int incY = 50;

which are used in a loop to produce the image below.

Changing the window size to 400 x 400 produces this image.

Bonus

Create some graphical patterns using loop.

For example using the values of Loop 3 above for the rectangle width the following image is produced.