CS 200 - Week 2 Jim Williams, PhD

Society of Women Engineers "Not just for women and not just for engineers; all students are welcome. We are especially looking for more computer science students!" - Emile Wille (Marketing Officer for SWE)

This Week Team Lab: Tuesday or Wednesday Program 1: Due Thursday Lecture: Primitive Data Types and Expressions

Team Labs First meeting this week. 1350 cs and 1370 cs Meet TAs & LAs 1st floor, around corner from elevators Meet TAs & LAs Work in small groups and pairs Discuss Terms, Trace & Explain code Edit-Compile-Run Cycle on the command-line

Pair Programming 2 people working together on 1 computer. One person types, the other provides direction and reviews. Many report more confidence in solution and more enjoyment programming. Important to switch roles (who has the keyboard). Provide respectful, honest and friendly feedback.

Learning to Trace with Java Visualizer Java Visualizer available via our course website or: https://cscircles.cemc.uwaterloo.ca/java_visualize/ import java.util.Scanner; public class RectangleArea { public static void main(String [] args) { Scanner input = new Scanner(System.in); int height = 0; int width = 0; System.out.print("Enter height: "); height = input.nextInt(); System.out.print("Enter width: "); width = input.nextInt(); int area = height * width; System.out.println("A rectangle with height " + height + " and width " + width + " has an area of: " + area); input.close(); return; //optional at end of method, unless returning value }

Programming Process Users Files Programmer Editor (Virtual) Compiler Machine Compiler Hello.java Hello.class Computer Files Programmer

Programming Errors Naming/Saving Syntax/Compile time Runtime & Logic Editor (Virtual) Machine Compiler Hello.java Hello.class Computer Files Programmer

Edit-Compile-Run Cycle From the command-line: notepad javac java

Programming Process Question Cat.txt Cat.java Cat.class Cat For the class named Cat, what is the name of the file that the compiler creates and is provided to the Java Virtual Machine to run?

Learning Programming Lots of little steps that quickly build Not mastering little steps creates bigger steps Goes beyond Remembering and Understanding to Applying, Analyzing, Evaluating and Creating. Goal: Have basic fluency in Java and be able to solve small problems using it.

Primitive Data Types int whole numbers (4 bytes) double floating point numbers (8 bytes) char single character (2 bytes) boolean true or false value (>= 1 bit) less commonly used: float (4), long (8), short (2), byte (1)

Primitive Data Type Conversion Which work? double a = 5; double b = 6.0; int c = 3.0F; float d = b; c = d; d = c; char e = 'A'; int f = e; short s = f; int h = 4 + 10 / 3; int i = 10.0 / 3; int j = (int) 10.0 / 3; double k = (int) 10.0 / 3.0

Operator Precedence & Associativity

Constant public class World { public static void main(String []args) { int size = 3; final int MAX_SIZE = 10; }

String class A reference (class), not a primitive data type. Frequently used final String TITLE_PREFIX = "Welcome to "; int week = 2; String welcome = "Week " + week; System.out.println( TITLE_PREFIX + welcome);

What are the values in a, b & c? int a = 5; int b = 7; int c = a; b = c; a = b;

What are the values in a, b & c? int a = 2; int b = 1; int c = a + b; a = b; a = c;

Swap values in a & b int a = 5, b = 3; Write code to swap values in a & b. a = b; b = a; c = b; b = c; c = a; a = c; Google "swapping values without third variable" for many creative ways.

Application: Temperature Conversion (Degrees Fahrenheit – 32) x 5 / 9 = Degrees Celsius What symbols have different meanings in Java? What changes must be made to implement this equation in Java? Retrieval practice importance of committing to an answer

My List X vs * equals (==) vs assignment (=) value is stored on the left hand side of assignment (=) operator Variables: name areas of computer memory, declare before use, declare type of data, initialize Variable names: start with letter, include letters numbers and _, but no spaces Conventions: camelCasing, spell out names Semicolon at the end of statements

CS Core Principles: Algorithms: A step-by-step set of operations to be performed. Analogy: Recipe, Instructions Abstraction: a technique for managing complexity. Analogy: Automobile, CS200 Computer View

Methods Lots of existing code that you can use rather than writing yourself. To use, "call the method". The method executes (runs) and may return a value.

Calling Class (static) Methods double numInts = Math.pow( 2, 32); double root = Math.sqrt( 16); int num1 = 16; int num2 = 3; double result; result = num2 + Math.sqrt( num1);

Defining Methods public class M { //method definition static void mPrint() { System.out.println("my print"); } public static void main(String []args) { M.mPrint(); // method call. B is the correct answer

mPrint - which is Call, Definition? mPrint call then mPrint definition static void mPrint() { System.out.println("my print"); } public static void main(String []args) { mPrint(); B is the correct answer

Argument vs. Parameter static void printCount(int count) { public static void main(String []args) { int num = 10; printCount( 23); printCount( num+3); } static void printCount(int count) { System.out.println( count); count is a parameter (zyBooks) or formal parameter the number 23, for example is an argument (also called an actual parameter).

Is count: Argument or Parameter? public static void main(String []args) { int num = 10; printCount( 23); printCount( num+3); } static void printCount(int count) { System.out.println( count); argument parameter count is a parameter (zyBooks) or formal parameter the number 23, for example is an argument (also called an actual parameter).

Returning a Value from a Method static int triple(int num) { return num * 3; } public static void main(String []args) { int value = 5; int result = triple( value);

Which is called first: calc or println? error static int calc(int num) { num -= 33; return num; } public static void main(String []args) { int n = 55; System.out.println( calc( n)); put a print statement within the calc method to see if it is called before the println method.

What prints out? static void calc(int num) { num = 3; } 5 35 error static void calc(int num) { num = 3; } public static void main(String []args) { int n = 5; calc( n); System.out.println( n); try it.

Return to Converter double degreesCelsius; double degreesFahrenheit = 100.0; degreesCelsius = (degreesFahrenheit - 32.0) * 5.0 / 9.0;