FSEM 131 Lab 2

Repetition

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To review the lecture material download the posted code and the references pages on while loop.

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1. [2 pts] Consider the following program that uses a while loop to print increasing numbers on the console.

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

The synthax for a while loop is the following

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

Now that you understand the process of a while loop, 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 a second while loops.
• Add the while loop below the provided code, such that
  this new loop 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 down with a while loop
12 11 10 9 8 7 6 5 4 3 2 1 0 
done: out of the while loop

2. [4 pts] Using a while, write a program moreLoops that produces on the console the output below for Loop 1 and Loop 2. You should write down your thought process first on a piece of paper. Check manually the loop iterations before pressing the run bitton. Pay attention to bounds (where the repetition starts and ends).

Loop 1 
0 3 6 9 12 15 18 

Loop 2
20 15 10 5 0 

2. [4 pts] Write a program ellipseLoop.pde that creates an output similar to the image below.

• The application window is 260 X 260 pixels.
• The background is white.
• The circles are centered in the window.
• The smaller circle is 40 by 40.
• The circles are separated by 20 pixels.

3. [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.

4. [4 pts] Write a program manyLinesGrid.pde that uses a for loop to create an output similar to the image below.

• The application window is 200 pixels wide and 200 pixels high.
• The lines are separated by 10 pixels in each direction: horizontal and vertical.
• The padding (space around the grid) is 20 pixels on all the sides.

The grid should be centered in the window with space all around.