Lecture by: Hugo Johnson INTRODUCTION TO PROGRAMMING PART I

Transcription

1 Lecture by: Hugo Johnson INTRODUCTION TO PROGRAMMING PART I

2 WHY BOTHER LEARNING TO PROGRAM A COMPUTER? For the fun To fill a need For a new or second Career As an intellectual challenge

3 PROGRAMMING IS PROBLEM-SOLVING To tell a computer how to solve one big problem, you usually must tell the computer how to solve a bunch of little problems that make up the bigger problem. If you want to make your own video game, for example, you need to solve some of the following problems: Determine how far to move a cartoon figure. Detect whether the cartoon figure bumps into a wall, falls off a cliff, or runs into another cartoon figure on-screen. Make sure that the cartoon figure doesn t make any illegal moves, such as walking through a wall. Draw the terrain surrounding the cartoon figure and make sure that if the cartoon figure walks behind an object such as a tree, the tree realistically blocks the figure from sight. Determine whether bullets that another cartoon figure fires are hitting the player s cartoon figure. If so, determine the amount of damage, how it affects the movement of the damaged cartoon figure, and how the damage appears on-screen.

4 PROGRAMMING IS PROBLEM SOLVING The simpler that the problem is that you need to solve, the more easily you can write a program that tells the computer how to work. Otherwise the more complex the problem, the bigger the program and it takes more time to be written.

5 PROGRAMMING IS LIKE WRITING ENGLISH ESSAY OR GIVING DIRECTIONS: If you can write step by step instructions directing someone to your house, you can write a program. The hardest part about programming is identifying all the little problems that make up the big problem that you re trying to solve. Eg. Giving some simple directions to someone: Go south on Highway I-5. I5 Get off at the Sweetwater Road exit. Turn right at the light. Turn into the second driveway on the left.

6 PROGRAMMING IS LIKE WRITING ENGLISH ESSAY OR GIVING DIRECTIONS: Of course, if you try giving these instructions to a computer, the computer gets confused and wants to know the following additional information: Where do I start and exactly how far south do I drive down Highway I- 5? How do I recognize the Sweetwater Road exit, and how do I get off at this exit? After I turn right at the light, how far to the right do I turn, and do you mean the traffic light or the street light on the corner? After I turn into the second driveway on the left, what do I do next? Park the car? Honk the horn? Gun the engine and accelerate through your garage door?

7 PROGRAMMING IS LIKE WRITING ENGLISH ESSAY OR GIVING DIRECTIONS: Unless you specify everything that you want the computer to do and exactly how to do it, the computer just plain doesn t do what you want it to do. N.B. A collection of instructions that tell the computer what to do is known as a program. The instructions, written in a specific programming language, is, p p g g g g, known as the source code.

8 WHY SO MANY DIFFERENT PROGRAMMING LANGUAGES? You have many programming languages to choose among because each language serves a specific purpose, and people are always creating new languages to solve different types of problems. Essentially, computers really understand only one language, which consists of zeroes and ones, also known as machine language. A typical program that you could write in machine language might look something like the following example:

9 MACHINE LANGUAGE HAS THE FOLLOWING TWO MAJOR DRAWBACKS: You can easily type a 0 or 1 by mistake, thereby preventing you from giving the computer the correct instructions. Machine language takes a long time to write (and an even longer time to understand d what the language is actually telling the computer to do). Because of these two huge problems, few people write programs in machine language. To make writing a program easier, programmers quickly invented asimpler programming language known as assembly language. g

10 EXAMPLE OF ASSEMBLY LANGUAGE CODE: title Nap Program ; This program displays Take a nap! on the screen dosseg.model small.stack 100h.data my_message db Take a nap!,0dh,0ah, $.code main proc mov ax,@data mov ds,ax mov ah,9 mov dx,offset my_message

11 UNDERSTANDING ASSEMBLY LANGUAGE Because computers can t read assembly language instructions, programmers created special programs that translate assembly language into machine language. These special programs are known as assemblers.

12 TWO DISTINCT ADVANTAGES OVER MACHINE LANGUAGE: Assembly language programs are easier to read than machine language programs. A bl l g g g i t Assembly language programs are easier to write (and modify) than machine language programs.

13 ASSEMBLY LANGUAGE HAS THE FOLLOWING DISADVANTAGES: Programs that t you create by using assembly language g run slower and gobble up more space (both physical disk space and memory) than equivalent programs that you may create with machine language. You can t easily transfer (or, to use programming lingo, port) a program that you write in assembly language for one computer to another computer. Writing a program in assembly language can prove extremely tedious, time-consuming, and complicated. That s why few people bother to write large programs in assembly language.

14 THE HOLY GRAIL OF PROGRAMMING N.B. In general, the easier the programming language is to read and write, the slower and larger are the programs it creates. The Holy Grail of computer programming is to create programs that t are easy to write, run as fast as possible, and take up as little space as possible.

15 WHAT ARE HIGH LEVEL LANGUAGES? Is it s a language that closely resembles English like statements and mathematic notations. It is independent of the internal machine code of any particular computer. The program written in High Level Language is called the Source Code while the translated version is called the Object Code.

16 EXAMPLE OF SOURCE CODE: main() { printf ( Take a nap!\n ); } This language g is known as C programming glanguage.the g above program is equivalent to the assembly language program for taking a nap. Not to worry about knowing the Syntax for now, it will all come to fruition. N.B. The Object code is really the raw 0s and 1s that the machine understands, in other words it s the machine code.

17 HIGH LEVEL LANGUAGES ARE SLOWER TO CREATE A program that you write in C runs slower and creates larger program files than does an equivalent assembly language program. That s because assembly language is closer to the native language of computers (which is machine code) d)than C. So C programs need to first get translated into assembly language code before finally being converted into machine language code.

18 KEY ADVANTAGES OF HIGH LEVEL PROGRAMMING LANGUAGES: It is easier to learn and code programs because the programmer does not need detailed knowledge of the computer or its internal operation. Errors are easier to avoid and detect. t Many high level languages are machine independent, making them portable (transferable from say a Mac to a PC or even a Smart Phone). Easier to maintain and shared with other programmers.

19 KEY DIS-ADVANTAGES OF HIGH LEVEL PROGRAMMING LANGUAGES: Takes longer to create because of the steps it has to take: converting from source code to assembly language code and then to machine code. Gives the user access to the computer s memory, which h has disastrous effects if misused.

20 THERE TWO WAYS TO CONVERT SOURCE CODE INTO OBJECT CODE: Using a Compiler: Translates to Object Code which is stored for processing at a later time. Using an Interpreter: Translates and runs the program in real time, object code created while program is being executed.

21 DIAGRAM OF SOURCE CODE TRANSITION TO MACHINE LANGUAGE

22 WHAT ARE FOURTH GENERATION LANGUAGES? It is type of Language that consists of more English like commands Which makes it easier to deploy a program vs its predicecer languages. A Perfect example would be the language SQL (Structured Query Language) Used in most Database Management System Software.

23 OBJECTIVES OF 4GLS: I th d f g d l t Increase the speed of program development Minimizing the end-user effort to obtain information from a computer. Decreasing the skill level required of end users, so they can concentrate on an application rather than on the intricacies of coding. They can therefore solve their own problems without the aid of a professional programmer. Minimize the maintenance by reducing errors and making programs easy to change.

24 NATURAL LANGUAGES Its a language that makes computer language as close to human As possible, allowing computers to interpret real English sentences. For example, if a user enters the command Get me sales Figures for January 2009, a computer understanding natural languages Could interpret this and supply the desired information. Read more on Natural language processing (NLP).

25 END OF LECTURE In our next lecture (Part II) we will focus on algorithm Development and its rules and principles.