CS 136 - Lecture 1

1. Why take CS 136?
2. The team
3. Sample problems
4. Your responsibilities
5. Design vs. Coding from Tomassia
6. Java syntax for Pascal features
7. Sample program

Why take CS 136?

• How to implement algorithms and data structures in Java.

• How to evaluate and visualize data structures and algorithms.

• How to design large programs (in an object-oriented way) so that it is easy to modify them.

The team

Course web page: http://www.cs.williams.edu/~andrea/cs136/

Sample problems

1. Write a backtracking algorithm to find a path from Williamstown to San Diego.
2. Find the shortest path from Williamstown to San Diego on interstate system

(and do it efficiently).
3. Schedule final exams so there are no conflicts.
4. Design and implement a scientific calculator.
5. Design and implement a simulator that lets you study traffic flow in a city or airport.

Your responsibilities

• Come to lectures.
• Do the reading in advance.
• After lectures review notes and study examples carefully until you understand them.
• Come to labs well-prepared with good designs. Most important time.
• Don't remain confused.
• Come see me during office hours when have questions on lecture material.
• Come see me or TA's when have questions about program.
• Head off problems before they become severe.
• Follow honor code guidelines.

I can present material to you to make it easier for you to learn.

• I cannot "teach" you.
• CS is not a spectator sport.

Design vs. Coding

Data Structure and Algorithm Design goals:

1. Correctness
2. Efficiency

Implementation Goals:

1. Robustness (produce correct output for all inputs - including erroneous input)
2. Adaptability (can evolve over time with new requirements - Y2K problem)
3. Reusability (use same code in multiple situations)

Java syntax for Pascal features

• Base types:

• boolean,
• char (16 bit),
• int (32 bit),
• long (64 bit),
• float (32 bit),
• double (64 bit);

• Distinguish int and long constants by adding "L" for long - e.g. 126L

• Distinguish float and double constants by adding "F" for float - e.g., 3.1415F

• Strings: "This is a string", + used for concatenation: "This is "+"a string."

• Results of string + anything is string: "#"+17 is same as "#17"

Brief review of the syntax for "traditional" constructs:

• assignment, "if", "for", "while", declarations, ==, !=, etc.

• Declarations not separated from rest of code

• type goes before variablename
• can be mixed with statements
• can be initialized in declarations
Example: int x = 17;
•  assignment x := e;  => x = e;
•  block begin ... end => {...}
•  "if" statement if => drop "then"
•  "while" statement while => drop "do"
•  "repeat" statement repeat .. until cond => do {...} while !cond;
•  "for" statement for i := 10 to 20 do => for (int i = 10; i <= 20; i++)
•  Semicolons are used as line terminator, not separator.
•  Comments

// starts comments which go to end of line
/* multi-line comments
    are done like this */

---

Sample Program

class SillyProgram{
    public static void main(String[] args){
        // void as return type means this is a procedure
        int sum = 0;
        for (int count = 1; count <= 10; count++){
            sum = sum + count;
        }
        if (sum > 50){
            System.out.println("Sum is big: "+ sum);
                    // + sum converts sum to string and concatenates
        } else {
            System.out.println("Sum is little: "+ sum);
        }
    }
}

We'll see later why "class", "public", "static" are used here.

Read: Chapter 3 of Core Java for more Java details.