Program Style Guide

Decimal vs Binary
Here are some equivalent values:

Binary Fingers

Try the following exercises:

2 Methods for binary-decimal conversions

Hexadecimal Number System

Octal Number System

More help

Octal to Hexadecimal conversion

Check edmodo.com for exercises.

Classwork:
Standard Drawing: Animation
Discussion on BouncingBall.java and Banner.java
Check on edmodo.com for assignment: CrossingBalls.java

Homework:
Check on edmodo.com for assignment: SongLyrics.java

Standard Drawing: Animation and images
Images. PU standard draw library supports drawing pictures as well as geometric shapes.

• Images. Our standard draw library supports drawing pictures as well as geometric shapes. The command StdDraw.picture(x, y, filename) plots the image in the given filename (either JPEG, GIF, or PNG format) on the canvas, centered on (x, y).
• Resources:

  https://introcs.cs.princeton.edu/java/15inout/TennisBall.png 
  https://introcs.cs.princeton.edu/java/15inout/pipebang.wav

• User interaction. Our standard draw library also includes methods so that the user can interact with the window using the mouse.
  

  double mouseX() return x-coordinate of mouse double mouseY() return y-coordinate of mouse boolean mousePressed() is the mouse currently being pressed?

  • • A first example. MouseFollower.java is the HelloWorld of mouse interaction. It draws a blue ball, centered on the location of the mouse. When the user holds down the mouse button, the ball changes color from blue to cyan. A simple attractor. OneSimpleAttractor.java simulates the motion of a blue ball that is attracted to the mouse. It also accounts for a drag force.
    • Many simple attractors. SimpleAttractors.java simulates the motion of 20 blue balls that are attracted to the mouse. It also accounts for a drag force. When the user clicks, the balls disperse randomly.
    • Springs. Springs.java implements a spring system.

  Standard audio.

  StdAudio is a library that you can use to play and manipulate sound files. It allows you to play, manipulate and synthesize sound.

  

  We introduce some some basic concepts behind one of the oldest and most important areas of computer science and scientific computing: digital signal processing.

  • Concert A. Concert A is a sine wave, scaled to oscillate at a frequency of 440 times per second. The function sin(t) repeats itself once every 2π units on the x-axis, so if we measure t in seconds and plot the function sin(2πt × 440) we get a curve that oscillates 440 times per second. The amplitude (y-value) corresponds to the volume. We assume it is scaled to be between −1 and +1.
  • Other notes. A simple mathematical formula characterizes the other notes on the chromatic scale. They are divided equally on a logarithmic (base 2) scale: there are twelve notes on the chromatic scale, and we get the ith note above a given note by multiplying its frequency by the (i/12)th power of 2.

  

  • When you double or halve the frequency, you move up or down an octave on the scale. For example 880 hertz is one octave above concert A and 110 hertz is two octaves below concert A.
  • Sampling. For digital sound, we represent a curve by sampling it at regular intervals, in precisely the same manner as when we plot function graphs. We sample sufficiently often that we have an accurate representation of the curve—a widely used sampling rate is 44,100 samples per second. It is that simple: we represent sound as an array of numbers (real numbers that are between −1 and +1).
  •  

  For example, the following code fragment plays concert A for 10 seconds.

  int SAMPLING_RATE = 44100; double hz = 440.0; double duration = 10.0; int n = (int) (SAMPLING_RATE * duration); double[] a = new double[n+1]; for (int i = 0; i <= n; i++) { a[i] = Math.sin(2 * Math.PI * i * hz / SAMPLING_RATE); } StdAudio.play(a);

  • Play that tune. PlayThatTune.java is an example that shows how easily we can create music with StdAudio. It takes notes from standard input, indexed on the chromatic scale from concert A, and plays them on standard audio.

2D Arrays

Additional programming style guidelines:

/* 
 * 1. Make sure your program has indentation when is needed.
 * 2. Please include a comment line about local variables and group them all 
 *    together at the top of the program as long as it is not an OOD program.
 * 3. Never create a new local variable inside a loop!
 * 4. Have a blank line between different parts of the program
 */

final int COUNTRIES = 7;
final int MEDALS = 3;
int[][] counts = new int[COUNTRIES][MEDALS];

or but not both:

int[][] counts = {
 { 1, 0, 1 }, 
 { 1, 1, 0 }, 
 { 0, 0, 1 }, 
 { 1, 0, 0 }, 
 { 0, 1, 1 }, 
 { 0, 1, 1 }, 
 { 1, 1, 0 }
 };

for (int i = 0; i < COUNTRIES; i++)
{
  // Process the ith row
  for (int j = 0; j < MEDALS; j++) 
  {
      // Process the jth column in the ith row
      System.out.printf("%8d", counts[i][j]); 
  }
  System.out.println(); // Start a new line at the end of the row 
 }

for (int i = 0; i < counts.length; i++) 
{
  for (int j = 0; j < counts[0].length; j++) 
  {
     System.out.printf("%8d", counts[i][j]); 
  }
  System.out.println(); 
}

Accessing the neighboring elements of a 2D array

Adding by rows:

int total = 0;
for (int i = 0; i < COUNTRIES; i++)
{
  total = 0;
  for (int j = 0; j < MEDALS; j++) 
  {
    total = total + counts[i][j];
  }
}

Adding by columns:

int total = 0;
for (int j = 0; j < MEDALS; j++)
{
  total = 0;
  for (int i = 0; i < COUNTRIES; i++) 
  {
    total = total + counts[i][j]; 
  }
}

Classwork:
Write a program, MedalsTable_YI.java to produce the following output:

Assignment:
Consider as an example an 8 × 8 array for a board game:
int[][] board = new int[8][8];

BoardGame_YI.java: Using two nested loops, initialize the board using "for" loops so that zeroes and ones alternate, as on a checkerboard. Prompt the user for the size of the "square" 2D array and display the board on the screen.

0 1 0 1 0 1 0 1
1 0 1 0 1 0 1 0
0 1 0 1 0 1 0 1
...
1 0 1 0 1 0 1 0

Hint: Check whether i + j is even.

Content for some questions:

1. Overflow

From

The int data type is a 32-bit signed two’s complement integer. It has a minimum value of -2,147,483,648 (0x80000000) and a maximum value of 2,147,483,647 (0x7FFFFFFF) (inclusive)

So when you add one to an integer’s max value:

0x7FFFFFFF + 0x00000001 = 0x80000000 (-2,147,483,648)

• Typical array-processing code.
• Programming with arrays.
  • Zero-based indexing
  • Array length
  • Memory representation
  • Bounds checking
  • Setting array values at compile time
  • Setting array values at run time
• Shuffling and sampling
  • Exchange
  • Shuffling
  • Hardwired constants
  • Sampling without replacement

classwork:
Write a program, ArrayBasics_YI.java to do the following:

1. Create an array a[] size 10. Assign a random number between 1 and 30 to each element.
   a. Display the first element of the array.
   b. Display the last element of the array assuming you do not know the size of the array.
   c. Display the messages given when you try to access an element with a negative index and with an index beyond the size of the array.
2. Create two arrays, suit[] and face_value[].
   a. The suit[] array contains the 4 different suits as elements.
   b. The face_value array contains “2”, “3”,…,”Jack”,…,”Ace” elements.
   c. Use the random function to select five cards and display them.
3. Create two arrays x[] and y[] with N number of elements both. Prompt the user for N. Assign random integers to each element. Then have another loop to find the product of each element wit the same index and add them all together. This operation is called the “dot product”.

Assignments:
ClosestPair_YI.java
Write a program to create an array of 100 random integers between the values of 1 and 1000 and find the two consecutive integers with the smallest difference between the two of them.

MaxInArray_YI.java
Write a program to create an array of 100 random integers between the values of 1 and 1000 and find the largest value.

AverageArray_YI.java
Write a program to create an array of 100 random integers between the values of 1 and 1000 and find the average of all the elements of the array.

PrintArray_YI.java
Write a program to create an array of 100 random integers between the values of 1 and 1000 and print them separated by 3 spaces. Note: Use printf to keep all your numbers tab properly.
A printf format reference page (cheat sheet)

Pop Quiz Array 1
Pop Quiz 1: Fix the problem