Elementary Programming

Elementary Programming Introduction

In today’s session… • What is programming? • Why should I learn programming? • Course Outline • Introduction to Programming Language • Introduction to Pascal • ‘Hello world!’ • ‘Hello, <your name>!’ • Variables

What is programming? • Process of writing, testing, debugging/troubleshooting, and maintaining the source code of computer programs (From Wikipedia) • To create a program (software) for usage of a particular sort, e.g. word processor (e.g. Microsoft Word, OpenOffice.org Writer) for word processing (duh)

Why should I learn programming? • Logic skills – very useful in Maths/Physics/Chemistry/… • Understand more about computer / information systems • Learn algorithms • Learn how to type – fast! • Represent the school in HKOI/CCC

Course Outline • Introduction 3/5 • Pascal Syntax – I 6/5 • Pascal Syntax – II 10/5 • Pascal Syntax – III (depends on schedule) 13/5 • Algorithms – I 17/5 • Algorithms – II (depends on schedule) 20/5 • HTML 24/5 • CSS 27/5 • PHP 31/5

Introduction to Programming Language • Derived from human language • Syntax – grammatical rules • Symbol-like • Lots: Pascal, A+, A++, B, C, C--, C++, C#, D, D#, E, F, F#, J, J++, J#, K, L, L++, M, Q, R, R++, S, T, X++, Y, Z, VB, ActionScript, PHP, FORTRAN, Java, Javascript, Python, etc. • For different purposes and with different syntax / ideology behind programming

Introduction to Pascal • ‘Educational’ • Syntax are human-like, easy to understand • Important in programming • Have practical use despite criticisms

Hello, world! • Classic approach to any programming language • Objective: Print ‘Hello, world!’ • Code: program hello; var a : integer; begin writeln(‘Hello, world!’); end.

Hello, world! • Analysis • program hello; • ‘;’ : to separate different statements • ‘program’ : a special keyword, to specify the name of the program • ‘hello’: the name of the program • * this statement can be ignored totally. • * note any ‘name’ cannot be special keywords or start with numbers. E.g. program 3x; or program program; is not valid, but program _3x; or program _program; is valid.

Hello, world! • Analysis (cont.) • var a : integer; • ‘var’ : a special keyword, to notify the following statements are declaration of variables • ‘a’: the name of the variable • ‘:’: declare ‘a’ is which type of variable • ‘integer’: a type of variable, which is integers (with range -32768..32767) • * this statement can be ignored totally since this program has no use of variables • * note program hello; var a : integer; is valid. • * note var a, b, c : integer; is valid.

Hello, world! • Analysis • begin writeln(‘Hello, world!’); end. • ‘begin’ : to specify the beginning of the program • ‘writeln’ : a function, to write the value then with a line break • * Try this out: writeln(‘Hello’); write(‘Hello’); writeln(‘Hello’); • (What is the difference between writeln() and write()?) • writeln; is valid (what does this do?) • ‘’’: to specify that the worlds ‘Hello, world!’ is a string, i.e. a series of characters, but not a variable. • *writeln(‘Hello’); and writeln(Hello); • ‘end.’: to specify the end of the program

Hello, <your name>! • Objective: Print ‘Hello,’, then the name of the user who has inputted his/her name in the first place. • Code: program hello; var name : string; begin write(‘Please input your name: ’); readln(name); writeln(‘Hello, ‘, name, ‘!’); end.

Hello, <your name>! • Analysis • var name:string; • ‘string’ : a type of variable, which is the compilation of characters • ‘name’: the name of variable of string • * Variables come in different kinds, e.g. for integers, we have integer, longint, int64; for characters, we have char; for string, we have string, ANSIstring. • * Each type of variables have different operations. • * Variable can be assigned by ‘:=‘. E.g. name := ‘This is my name’ or a := 3; • Note that ‘’ is added to state that the values inside is a string! • a := a + 1 is possible!

Hello, <your name>! • Analysis • readln(name); • ‘readln’ : to request input of variable to the user • ‘name’: the name of variable of string • * Try read(name); instead of readln(name);, Or guess what’s the differences between readln and read.

Hello, <your name>! • Analysis • writeln(‘Hello, ‘,name,’!’); • ‘,’ is used to separate strings and values in the variable ‘name’ • * writeln(‘H’,’e’,’l’,’l’,’o’,’,’,’ ‘,’); is equivalent to writeln(‘Hello,’);

Variables • Integral types (0, 1, 2, 3, …) • Shortint (-128..+127) • Byte (0..255) • Integer (-32768..+32767) • Word0 (-65536..65535) • Longint(-2146473648..+2146473647) • Floating point types (0.1, 0.23, etc.) • Real • Double

Variables • Operations of Integral / Floating point types • ‘+’, e.g. c := a+b; • ‘-’ e.g. c := a-b; • ‘*’ e.g. c := a*b; • ‘/’ e.g. c := a/b; • ‘div’ e.g. c := a div b; • ‘mod’ e.g. c := a mod b; • ‘()’ e.g. c := (a + b)*a;

Variables • Non-numerical • Char (characters, e.g. ‘a’, ‘A’, ‘!’) • String (an array of characters, usually max. at 255) • Array (a collection of variable of specific types with index) <- covered later • Operations • chr(x); Convert ASCII code (x) into character • ord(c); Convert character (c) into ASCII code • length(str); Find the length of a string (str) • copy(str, x, y); Copy, starting from the xth element, y elements of string (str) • pos(substr, str); Find position of substr in str • val(str, x, e); Convert a string (str) into an integer (x) • str(x, str); Convert an integer (x) into a string (str) • concat(str1, str2, …); Combine a string (str1) with another (str2, etc.) • insert(str1, str2, x); Insert a string (str1) in the xth element of another (str2) • delete(str, x, y); Delete, starting from xth element, y elements of string (str) • fillchar(str, x, c); Fill the string (str) with a character (c) until string is (x-1) long

Last but not least… • Pascal compilers: • Free Pascal (Official HKOI/CCC compiler) • Dev-Pascal • Quick Pascal • Useful software: • Notepad++ • Useful website/contact: • http://www2.dbs.edu.hk/club-soc/ecs • Lin Yin Long (L6D)

Elementary Programming