Minute Paper 03/30/2009 

1. Username, name
2. Status of your homework
3. What is it that you need that you don't
have yet (that I could then try to provide for
you) to make the most out of this course (and do 
your assignments) or things to that effect? 

Assignment Two, problem 1:

a) the main method receives an array of strings argument
which includes the command line arguments. So in a set up
like this:

class One {
  public static void main(String[] args) {
    
  }
}

inside main you can refer to args.length (which will 
evaluate to the number of elements in the array of strings
called args that main receives) and with an index i in between
0 and args.length - 1 you can access any individual string
element of the array args that main receives as args[i]

class One {
  public static void main(String[] args) {
    int count = 1;
    for (int i = 0; i < args.length; i++) {
      System.out.println(count + ". " + args[i]); 
      count += 1; 
    }  
    // if we want to store them, where do we store them 
    int[] nums = new int[args.length]; // initialized to 0's
    // declare nums as an array of ints, allocate that many cells
    for (int i = 0; i < nums.length; i++) {
      System.out.print(nums[i] + " ");  
    } 
    System.out.println(); 
    // so this prints the values in nums, separated by blanks
    // all of them on the same line

    // next we set the locations in nums to be the converted 
    // corresponding values in args 
    for (int i = 0; i < args.length; i++) {
      nums[i] = Integer.parseInt(args[i]); 
    } 
    // print the array, so we can see the numbers we just stored
    for (int i = 0; i < nums.length; i++) {
      System.out.print(nums[i] + " ");  
    } 
    System.out.println(); 

    // change them by adding 2 to each one of them
    for (int i = 0; i < args.length; i++) {
      nums[i] += 2; // nums[i] = nums[i] + 2; 
    } 
    // show the array with modified numbers again 
    for (int i = 0; i < args.length; i++) {
      System.out.print(nums[i] + " ");  
    } 
    System.out.println(); 
    
  }
}

So you see how you can read (Strings and convert them into) ints
from the command line. Question is now: how do you rearrange them? 

class One {
  public static void main(String[] args) {
    int[] n; // declare variable n as referring to an array of ints
    n = new int[10]; // creates an array of ten locations and assigns
                     // it to n so you can use n[i] to refer to them
    n[4] = 5; // n[4] is the 5th location, changes now from 0 to 5

    // declare a variable to refer to a two dimensional array
    int[][] m; // variable to a matrix, two dimensional array of ints
    // allocate storage
    m = new int[4][5]; // a 4 by 5 matrix of numbers
 
    int size = 12;

    m = new int[size][size]; // m being an array of arrays 

    m[3][4] = 9; 

    for (int i = 0; i < m.length; i++) {
      for (int j = 0; j < m[i].length; j++) {
        System.out.print(m[i][j] + " "); 
      }  
      System.out.println(); 
    } 
    
  } 
}

So for Wednesday: 

a) problem one -- you know how to read a sequence of numbers from
the command line, that includes some conversions, can you rearrange
them in some fashion? 

b) problem two -- do you understand the rules? can you build a 5x5
magic square by hand? can you do it now that you know how to handle
a two dimensional array of integers in Java?