CONTENTS: What Is Programming? How a Computer Works Programming Languages Java Basics. COMP-202 Unit 1: Introduction

Transcription

1 CONTENTS: What Is Programming? How a Computer Works Programming Languages Java Basics COMP-202 Unit 1: Introduction

2 Assignment 1 Assignment 1 posted on WebCt and course website. It is due September 22nd st at 23:30

3 Tutorial 0 Help with setting up your computer to compile and run a Java program Trottier room 3120 See course website for more details on schedule.

4 Last Class Solving many little problems to avoid thinking about too much at once! A tiny bit about java

5 Correction from Last Class The Inuit actually did NOT have several dozen words for snow. This is a misnomer. The Sami people did have many. imo_words_for_snow

6 Today What is programming? How computers think A tiny bit more about java: The structure of a program

7 Part 1: What Is Programming?

8 Programming and Computers In order to understand what programming is, we need to know what a computer is COMP Introduction 8

9 Programming and Computers In order to understand what programming is, we need to know what a computer is A computer is a machine that executes lists of instructions We feed a list of instructions to the computer and the computer executes them The computer may apply the instructions on additional information fed to the computer (the input) The computer may produce information as a result of executing this list of instructions (the output) COMP Introduction 9

10 Programming and Computers Programming a computer involves two things: 1) Designing lists of instructions that will make the computer solve specific problems (a.k.a. writing your program) 2) Having the computer execute the instructions (a.k.a. running your program) COMP Introduction 10

11 Why do we want to program? Before we go any further, it's important to answer the question: What's the benefit of programming? COMP Introduction 11

12 Why do we want to program? COMP Introduction 12

13 Benefits of programming Programming computers allows us to sleep much more easily knowing that nothing ever could go wrong. Our programs will always work perfectly and will never crash or make any sort of mistakes. COMP Introduction 13

14 Actually...maybe not Anyone used Windows Vista? COMP Introduction 14

15 Benefits of programming All jokes aside, generally we program computers because we either can't or don't want to do the task ourselves. Some reasons: -very repetitive task -arithmetic of large numbers -searching through millions of documents -having someone help us without having to bother a real human -playing a game against a computer -researching information COMP Introduction 15

16 Giving a computer instructions A very good way to think about giving a computer instructions is the following: 1)First figure out what is given in the problem and where it is you are trying to go. 2)Figure out a broad picture of how you want to get from your start to the goal. When you do this, you should figure out, at each step, what you are given, and what you want to produce. Now you have several, smaller problems. You can solve the smaller problems the same way. COMP Introduction 16

17 Example: Planning Dinner Start: We need to construct a path from the start to the goal Goal: COMP Introduction 17

18 Example: Planning Dinner Start: Goal: COMP Introduction 18

19 Giving a computer instructions At each partial step, we need to make sure we have very precisely determined what we have at the moment and what we need to produce in that step. For example: Step 1)Shopping: We have : a recipe a burning desire to eat food money We want to produce: raw ingredients COMP Introduction 19

20 Giving a computer instructions Here we can also notice that one of the things we have is not really needed to solve this partial problem. For example: Step 1)Shopping: We have : a recipe a burning desire to eat food money We want to produce: raw ingredients COMP Introduction 20

21 Giving a computer instructions At each partial step, we need to make sure we have very precisely determined what we have at the moment and what we need to produce in that step. Step 2)Chopping: We have : raw ingredients We want to produce: chopped ingredients What is very important about this? COMP Introduction 21

22 Giving a computer instructions Step 2)Chopping: We have : raw ingredients We want to produce: chopped ingredients The input of step 2 is part of the output of step 1. This means that we can use it. If step 2 required something else (for example, if we also needed to buy knives), then this wouldn't be a complete solution. COMP Introduction 22

23 Giving a computer instructions At each partial step, we need to make sure we have very precisely determined what we have at the moment and what we need to produce in that step. Step 3)Cooking We have : chopped ingredients We want to produce: cooked food And we've found a path from one to the other. COMP Introduction 23

24 Giving a computer instructions When you are giving instructions to a computer, most of the time, you will repeat this divide and conquer process. For example: Shopping could be split into: 1)Pick up onions 2)Pick up bread 3)Pick up meat 4)Wait in line at the cash register 5)Pay the cashier etc. COMP Introduction 24

25 Giving the instructions to a computer Once you have mapped out a solution to a problem in small enough instructions, you can program a computer to execute the instructions

26 Two things to remember about computers 1)They require very specific instructions: -You can't tell a computer to cook dinner. It has to be much more detailed!

27 Two things to remember about computers 2)They interpret instructions very literally. -No sense of idioms as we do in human languages.

28 Amelia Bedilia COMP Introduction 28

29 Amelia Bedilia Draw the drapes Make a sponge cake Pitch the tent COMP Introduction 29

30 Human and Computer Languages Consider the following English sentence: "The lady hit the man with a baby" Does this mean 1)A lady hit a man who had a baby? (Dude, what a jerk!) 2)A lady used a baby to hit a man? (Good lord!) 3)A lady and a baby ganged up on a man and hit him. (Kids today!) Computer statements, on the other hand, always have only one possible interpretation although sometimes no one knows how a computer will interpret something! COMP Introduction 30

31 Human and Computer Languages One of the challenges is to learn the different interpretations the computer will give to commands. The computer will not normally tell you how it is interpreting things. It is up to you to figure it out, both by looking at your code and observing the output. COMP Introduction 31

32 Feedback from the computer If you omit the proper instructions or include the wrong instructions, generally 4 things can happen: 1)You get incredibly lucky and on that particular input it works anyway 2)The program gives the incorrect output 3)The program crashes 4)The program goes on forever and ever COMP Introduction 32

33 Java! Now, let's go over our very first program! COMP Introduction 33

34 Java Program: Hello World public class HelloWorld { public static void main(string[] args) { System.out.println("Hello World!"); COMP Introduction 34

35 Java Program: Hello World public class HelloWorld { public static void main(string[] args) { System.out.println("Hello World!"); One thing to notice is all these { and These are used to denote blocks of code. The purpose of a block is mainly to help the programmer keep track of what parts of code are related. COMP Introduction 35

36 Java Program: Hello World public class HelloWorld { public static void main(string[] args) { System.out.println("Hello World!"); {'s always mark the beginning of a block (or segment) of code. Each { always has a corresponding to mark the end. You can tell which corresponds to which because the first { opened, will correspond with the last COMP Introduction 36

37 Java Program: Hello World public class HelloWorld { public static void main(string[] args) { System.out.println("Hello World!"); Try at home: What happens if you remove the final, so that there are not matching braces? What happens if you add an extra at the end so that there are 3 s? COMP Introduction 37

38 Java Program: Hello World public class HelloWorld { public static void main(string[] args) { System.out.println("Hello World!"); Most (but not all) of the time, right before a { will be some code specifying what kind of block of code something is. For the first {, the code is public class HelloWorld COMP Introduction 38

39 class in Java public class HelloWorld { public static void main(string[] args) { System.out.println("Hello World!"); One of the key units of organizing things in Java is called a class. A class can have many different things in it which we'll see throughout the term. COMP Introduction 39

40 class in Java public class HelloWorld { public static void main(string[] args) { System.out.println("Hello World!"); Here we are saying: I want to create a class called HelloWorld and I want it to be public The first { signifies the start of the definition of the class The final signifies the end of the definition of the class COMP Introduction 40

41 Java Program: Hello World public class HelloWorld { public static void main(string[] args) { System.out.println("Hello World!"); On the second line we have another { In this case, the code before is defining a method COMP Introduction 41

42 methods in Java public class HelloWorld { public static void main(string[] args) { System.out.println("Hello World!"); A method is also a key unit of organization in Java. COMP Introduction 42

43 methods in Java public class HelloWorld { public static void main(string[] args) { System.out.println("Hello World!"); Here we are saying: I want to create a method called main There are several other words (public, static, void, String[], args) that we'll talk about later. COMP Introduction 43

44 methods in Java public class HelloWorld { public static void main(string[] args) { System.out.println("Hello World!"); The second { signifies the start of the method called main. The first signifies the end of the definition of the method called main. COMP Introduction 44

45 methods in Java public class HelloWorld { public static void main(string[] args) { System.out.println("Hello World!"); Since the definition of the method called main is inside the definition of the class called HelloWorld, it means that the method main is a part of the class HelloWorld. COMP Introduction 45

46 Methods and classes Almost every line of code you write in Java will be inside a class. This helps keep things nicely organized. Almost every line of code you write in Java will also be inside of a method. This also helps keep things nicely organized. Every method you ever write, will be part of a class. COMP Introduction 46

47 main method The main method is a very particular method. When you run a Java program, you actually run a Java class When you do this, the execution of your program will always start at the beginning of the method called main inside whatever class you run. COMP Introduction 47

48 Java Program: Hello World public class HelloWorld { public static void main(string[] args) { System.out.println("Hello World!"); Inside of a method, you can put many statements or commands. The highlighted line is an example of a statement. All statements in Java end in a semi-colon. COMP Introduction 48

49 Java Program: Hello World public class HelloWorld { public static void main(string[] args) { System.out.println("Hello World!"); The command System.out.println is a way to print something to the screen. It will print everything between ( and ) as long as it's on 1 line. COMP Introduction 49

50 Summary: -Important to break problems down into many pieces -Classes and methods are just 2 of the ways that Java helps us to organize things. These are important because they'll help make sure we don't need to think about too much at once. COMP Introduction 50

51 Homework Read the lecture titled unit1 on the course webpage. The material is mostly not directly examinable, but it's good to keep in mind while coding. COMP Introduction 51

52 Next Class Printing more complex statements Getting input from the user to make our programs more useful! COMP Introduction 52