CS 136 - Lecture 1

1. Why take CS 136?
2. 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?

Learn about designing correct and efficient algorithms and data structures

• learned to crawl in CSCI 134/135 - now learn to run

How to evaluate and visualize data structures and algos.

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

Team:

Course web page: http://www.cs.williams.edu/~kim/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 (if read in advance, will make more sense)

• 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 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 (produces correct output for all inputs - including erroneous input)

2. Adaptability (can evolve over time with new requirements - 2000 problem)

3. Reusability (Use same code in multiple situations)

Java syntax for Pascal features

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

Distinguish float and double constants by adding "f" or "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"

Briefly review syntax of "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;

  x := e; => x = e;

  begin ... end => {...}

  if => drop "then"

  while => drop "do"

  repeat .. until cond => do {...} while !cond;

  for i := 10 to 20 do => for (int i = 10; i <= 20; i++)

  begin ... end {...}

  Semicolons used as line terminator, not separator.

  // 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 hand-out and Chapter 3 of Core Java for more Java details.