Programming. Ed Milne

Transcription

1 Programming Ed Milne

2 Theme What is programming How its done The tools that are used

3 Programming Software is the instructions which tell your computer what to do Programming is the process of creating software

4 UML Universal Modelling Language Graphical way of describing program and system logic Can also be used for manual procedures There is freeware available for creating UML diagrams

5 UML Example

6 Objects Objects are independent entities that perform specific functions within a program A program that uses an object does not have to know how an object works

7 Objects Objects can be reused in many programs This reduces the programming effort If the object is successfully working in other programs it reduces the debugging effort Objects can also reduce the learning curve for software users e.g. the Open function in Windows programs Objects are used in other contexts such as word processing OLE = Object Linking and Embedding

8 Linking Programs are created as a series of separate modules rather than a single unit Linking resolves the addresses of the different modules so control can be passed between them The result of linking is an integrated program containing multiple modules A linker links the modules together

9 Dynamic Linking Some objects are linked into a program dynamically after it starts This reduces the time to start the program and the amount of RAM used Many programs have many options that are rarely used Dynamically linked modules are kept in Dynamic-Link Libraries (DLL) files

10 Programming Languages Used to tell the computer what to This is source code of programs A major goal is to reduce the human effort needed to create programs

11 Machine Language Machine language is the code used by the CPU This is just a series of bytes such as A0 12 FF 7E 3B Such code is time consuming to create and maintain

12 Assembly Language A human readable form of the machine language There is usually a one-to-one relationship between an assembly language source code and a machine instruction Assembly language is only used for the innermost loops where efficiency is critical It gives the finest control over the program instructions

13 Assembly Language An assembler converts the human readable code into machine code A disassembler converts machine code into human readable assembly language

14 Assembly Language Example.text.globl main main: la $a0, query #First the query li $v0, 4 syscall li $v0, 5 #Read the input syscall move $t0, $v0 #store the value in a temporary variable #store the base values in $t1, $t2 # $t1 iterates from m-1 to 1 # $t2 maintains a counter of the number of coprimes less than m sub $t1, $t0, 1 li $t2, 0 tot: blez $t1, done move $a0, $t0 move $a1, $t1 jal gcd #termination condition #Argument passing #Argument passing #to GCD function

15 Compiled Languages Compiled languages are higher level language A compiler converts the source code into machine code A decompiler converts machine code into a higher level language

16 Procedural Languages Before object orientated languages (OOP) procedural languages created a program as one complete unit Later versions were enhanced to create objects The most common procedural languages were COBOL and Fortran

17 COBOL COmmon Business Oriented Language is a procedural language used for business applications The syntax is based on the English language

18 COBOL Example IDENTIFICATION DIVISION. PROGRAM-ID. TEST. ENVIRONMENT DIVISION. DATA DIVISION 01 some-record. 05 num PIC 9(10). 05 the-date. 10 the-year PIC 9(4). 10 the-month PIC the-day PIC 99. PROCEDURE DIVISION IF invalid-record IF no-more-records NEXT SENTENCE ELSE READ record-file AT END SET no-more-records TO TRUE.

19 FORTRAN FORmula TRANslating system is a procedural language used for numeric and scientific calculations The syntax is based on algebra

20 FORTRAN Example program average! Read in some numbers and take the average! As written, if there are no data points, an average of zero is returned! While this may not be desired behaviour, it keeps this example simple implicit none real, dimension(:), allocatable :: points integer :: number_of_points real :: average_points=0., positive_average=0., negative_average=0. write (*,*) "Input number of points to average:" read (*,*) number_of_points allocate (points(number_of_points)) write (*,*) "Enter the points to average:" read (*,*) points

21 FORTRAN Example! Take the average by summing points and dividing by number_of_points if (number_of_points > 0) average_points = sum(points) / number_of_points! Now form average over positive and negative points only if (count(points > 0.) > 0) then positive_average = sum(points, points > 0.) / count(points > 0.) end if if (count(points < 0.) > 0) then negative_average = sum(points, points < 0.) / count(points < 0.) end if deallocate (points)! Print result to terminal write (*,'(a,g12.4)') 'Average = ', average_points write (*,'(a,g12.4)') 'Average of positive points = ', positive_average write (*,'(a,g12.4)') 'Average of negative points = ', negative_average

22 C Dennis Ritchie of Bell Labs developed 3 programming languages which he called A, B and C C was a success Enhanced versions were named C+ and C++ C++ is the current standard for hard core programming such as operating systems

23 C++ Example # include <stdio.h> int main(void) { printf("hello, world\n"); }

24 BASIC Beginner's All-purpose Symbolic Instruction Code wad initialized designed to teach programming to students Variants of BASIC underlay Microsoft Office, Open Office and LibreOffice There are many versions of BASIC

25 BASIC Example Public Class StarsProgram Public Shared Sub Main() Dim UserName, Answer, stars As String, NumStars As Integer Console.Write("What is your name: ") UserName = Console.ReadLine() Console.WriteLine("Hello {0}", UserName) Do Console.Write("How many stars do you want: ") NumStars = CInt(Console.ReadLine()) stars = New String("*", NumStars) Console.WriteLine(stars) Do Console.Write("Do you want more stars? ") Answer = Console.ReadLine() Loop Until Answer <> "" Answer = Answer.Substring(0, 1) Loop While Answer.ToUpper() = "Y" Console.WriteLine("Goodbye {0}", UserName) End Sub End Class

26 Interpreters Interpreters directly execute source code without converting it to machine code

27 JavaScript JavaScript is an interpreted language used in web pages An interpreted language is required because Web pages can only contain ASCII characters Pictures, sounds and videos are included by inserting a URL into the web page Special characters are included as strings of ASCII characters e.g. È for È Web designers want their pages to work on Widows, Linux, Mac, tablets and smart-phones without having to write separate versions for each type of device

28 JavaScript A JavaScript interpreter is included in web browsers JavaScript is a Write Once Run Anywhere (WORA) language

29 JavaScript Example <!DOCTYPE html> <meta charset="utf-8"> <title>minimal Example</title> <h1 id="header">this is JavaScript</h1> <script> document.body.appendchild(document.createtextnode('hello World!')); var h1 = document.getelementbyid('header'); // holds a reference to the <h1> tag h1 = document.getelementsbytagname('h1')[0]; // accessing the same <h1> element </script> <noscript>your browser either does not support JavaScript, or has it turned off.</noscript>

30 Java Java is a combination of a compiled and interpreted language The source code is compiled into executable code for Java's virtual CPU The compiled code is executed by the Java Runtime Environment (JRE) JREs are available for many different systems Like JavaScript Java is a WORA language

31 Java Java was intended to protect computers from malware The programs run in sandbox which is isolated from the rest of the computer Hackers have taken this as a challenge and the JRE is under constant attack

32 Java Example // This is an example of a single line comment using two slashes /* This is an example of a multiple line comment using the slash and asterisk. This type of comment can be used to hold a lot of information or deactivate code, but it is very important to remember to close the comment. */ package fibsandlies; import java.util.hashmap; * This is an example of a Javadoc comment; Javadoc can compile documentation * from this text. Javadoc comments must immediately precede the class, method, or field being documented. */ public class FibCalculator extends Fibonacci implements Calculator { private static Map<Integer, Integer> memoized = new HashMap<Integer, Integer>();

33 Java Example * The main method written as follows is used by the JVM as a starting point for the program. */ public static void main(string[] args) { memoized.put(1, 1); memoized.put(2, 1); System.out.println(fibonacci(12)); //Get the 12th Fibonacci number and print to console } * An example of a method written in Java, wrapped in a class. * Given a non-negative number FIBINDEX, returns * the Nth Fibonacci number, where N equals FIBINDEX. fibindex The index of the Fibonacci number The Fibonacci number */ public static int fibonacci(int fibindex) { if (memoized.containskey(fibindex)) { return memoized.get(fibindex); } else { int answer = fibonacci(fibindex - 1) + fibonacci(fibindex - 2); memoized.put(fibindex, answer); return answer; } } }

34 Debugging Most of the time and effort in programming is spent removing defects (bugs) rather than writing the code In spite of this, programs still have bugs The combinations and permutations of hardware and other software are too large to be tested Some software developers, like Microsoft, have their software send data back to them when it fails This lets them use their customers as unpaid

35 Macros Office and programs let you write code by recording your actions in a macro

36 LibreOffice IDE The Integrated Development Environment (IDE) lets you edit and test BASIC code The controls are Compile compiles the source code The LibreOffice Basic compiler is embedded in the application Run executes the compiled code after a break Stop stops executing the code Step Over steps over the next instruction Step Into execute the next instruction

37 LibreOffice IDE Step Out returns to the previous routine in the current macro Breakpoint stop executing when an instruction is reached or remove a breakpoint Enable Watch displays the variables in the current macro Insert Source Text inserts additional source code into the macro from a file In the large pane, you can edit the source code or enter new code You can find some useful functions online

38 LibreOffice Basic Function Function SmallIntToText(ByVal n As Integer) As String REM by Andrew D. Pitonyak Dim sonewords() Dim stenwords() Dim s As String If n > 999 Then Print "Warning, n = " & n & " which is too large!" Exit Function End If sonewords() = Array("zero", _ "one", "two", "three", "four", "five", _ "six", "seven", "eight", "nine", "ten", _ "eleven", "twelve", "thirteen", "fourteen", "fifteen", _ "sixteen", "seventeen", "eighteen", "nineteen", "twenty") stenwords() = Array( "zero", "Ten", "twenty", "thirty", "fourty", _ "fifty", "sixty", "seventy", "eighty", "ninety")

39 LibreOffice Basic Function s = "" If n > 99 Then s = sonewords(fix(n / 100)) & " hundred" n = n MOD 100 If n = 0 Then SmallIntToText = s Exit Function End If s = s & " " End If If (n > 20) Then s = s & stenwords(fix(n / 10)) n = n MOD 10 If n = 0 Then SmallIntToText = s Exit Function End If s = s & " " End If

40 LibreOffice Basic Function SmallIntToText = s & sonewords(n) End Function