CS 1 : Lecture 14

Lecture 14: Problem Solving, Arrays, and Topic Review

One more problem solving example.
Topic Review for the Midterm.
Introduction of today's lab assignment.

An Optimal Strategy For Nim

  - designing an optimal strategy for playing Nim
  - get a strategy and show why it's optimal
  - write down in comments the exact steps for performing that strategy
  - put that strategy into code
  - emphasize the use of logical structures: AND, OR, and NOT

  - go over topics for the midterm

Exam Format

You will have an entire normal class period to complete the exam. There will be 3 types of questions. Some will be of a form similar to true/false questions. Some will be of the form "what does this program output". For some you will have to write out code for small programs.

For the exam you will be able to bring in one normal-sized (8 1/2" x 11") page of notes. The notes can be on both sides of that page, but everything must be written by hand. No photo-copying. No typing.

HTML / CSS

Know the basic structure of an HTML document:

<html>
   <head>
   </head>
	
   <body>
   </body>
</html>

Know how to use the basic HTML tags: <p>, <title>, <h1>, etc.
Know the proper syntax for creating an HTML table, image, link, or list.
Know how to add a tag attribute (such as a class or id).
Know the basic format of and how to create a basic CSS rule: element {property: value;}
Know how to place the CSS rules in an internal style sheet (within the <style> HTML element). This includes knowing where to place the <style> tags.
If given some choices, be able to change a requested CSS property.
Remeber how colors were created (with RGB values). You'll need to remember, in a general sense, how RGB values worked.

Internet

See Lecture 4.

Graphs

Know that a graph is made up of vertices (also called nodes) which are connected by edges. Edges may be either directed or undirected.
A path through a graph is a traversal from some graph vertex, traveling along edges and through other vertices, until the desired goal vertex is reached. A path is simple if no vertex or edge is traversed more than once in the path.
A graph is connecte if every node can reach every other vertex (if all edges in the graph were treated as being undirected).
A cycle occurs if there is more than one simple path from a given vertex to any other vertex in the graph.
A tree is a graph without cycles. A tree can also have notions of a parent node and child nodes if we have directed edges.

Memory and Primitive Types

Computer memory is made up of bits, each of which can be set to 0 or 1. Bits can be organized into groups of 8 called bytes as well as larger groups. The same collection of 0's and 1's can represent a number, letter, boolean value, or even an instruction in a computer program.
Each of the 8 different primitive data types (byte, short, int, long, float, double, char, boolean) uses up a specific amount of memory. For example, a byte always uses up 8 bits of memory.
Know how to make arithmetic expressions. If you know operator precendence that's nice, but you can use parantheses if you don't. You'll need to know that numeric data types can overflow and what happens when they do. Also know that an integer division drops the remainder. Know when the (/) operator performs integer division and when it performs floating point division. Similarly, know when the (+) operator performs addition and when it performs string concatenation.
Know how to make boolean expressions. The logical AND (&&), OR (||), and NOT (!) operators are essential for longer, combined expressions. Also know that the AND and OR operators are short circuiting and how that can help you.
Know the proper form for the if, while, do-while, and for program statements as well as how to use each.

References To Objects

Know that a variable always holds either a primitive data type value or a reference to an object. Thus, what is the correct type of this variable: String name = "boozer";. The type of name is reference to a String object.
Remember the tricky things that can happen if you get aliasing, which is two or more variables that reference the same object. Also know what effects you can get when you pass references to objects as parameters to methods. This is an important topic and also a tricky one. You may be helped a lot to just always remember that a variable only stores the address of where the object is stored in memory. This can also be called a reference to that object. The actual object is stored somewhere else (never directly held by any variable).
You should know the String class. You will still need to know how to declare and initialize variables that reference String objects. Remembering that strings are immutable and understanding what that means would also be a good idea.
Understand the basics of method behavior (what happens when one is called), especially that parameters are passed by value. Know what that means and what effect it has for primitive data types and for references to objects.
Know how to figure the scope of identifiers, especially for variable names.
Remeber that a variable, or a method, can be used in place of a literal value. For example, instead of int x = 3; I could set x equal to some other variable with the type int or equal to some method that has a return type int.

Arrays

Know the basics of how to work with arrays. Recall that arrays are objects in case their used as parameters for any method. Know how to declare and initialize an array. Know how to access entries within an array. Also, remember that a single array only holds entries of a specific type (that is, a single array might hold either int's or String's, but not both).

Practice Questions

What is the output of the following program? (If the program would crash and not run, state that instead with a brief explanation why.)

   public static void main(String[] args){
	   
      String word1 = "hip-hop";
      String word2 = "hip";
      word2 = word2 + "-hop";
		  
      if(word1 == word2)
         System.out.println("The two strings are equal.");
      else
         System.out.println("The two strings are not equal.");
   }

What is the output of the following program? (If the program would crash and not run, state that instead with a brief explanation why.)

   public static void main(String[] args){
	   
      int num1 = 0;
      int num2 = 1;
      int num3 = 2;
		
		
      if(num1 > num2 > num 3)
         System.out.println("The numbers are in order.");
      else
         System.out.println("The numbers are out of order.");
   }

What is the output of the following program? (If the program would crash and not run, state that instead with a brief explanation why.)

   public static void main(String[] args){

      int num1 = 0;
		
      for(int i=0; i < 128; i++){
         num1++;
      }
	
      System.out.println("After incrementing " + i + " times, the value of num1 is: "+num1);
   }

Fill in the method below so that it returns the lowest value of the three input parameters.
```
   public static int findLowest(int num1, int num2, int num3){

   }
	
```