Mcs lec2
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This document discusses the evolution of programming languages from machine languages (1GL) to natural languages (5GL). It begins by defining a programming language as a formal notation system that describes computation in a readable and machine-readable form. It then categorizes generations of programming languages based on their level of abstraction, from low-level machine codes (1GL) to high-level languages (3GL) to domain-specific languages (DSL). The document provides examples and characteristics of languages from each generation.
Mcs lec2
- 1. What is a Programming Language? PS — Introduction © O. Nierstrasz 1 • A formal language for describing computation? • A “user interface” to a computer? • Syntax + semantics? • Compiler, or interpreter, or translator? • A tool to support a programming paradigm? A programming language is a notational system for describing computation in a machine-readable and human-readable form. — Louden
- 2. 2 Figure 9.2 Categories of programming languages
- 3. Generations of Programming Languages 1GL: machine codes 2GL: symbolic assemblers 3GL: (machine-independent) imperative languages (FORTRAN, Pascal, C ...) 4GL: domain specific application generators 5GL: AI languages … ( Prolog, OPS5, and Mercury are examples of fifth-generation languages.) Each generation is at a higher level of abstraction PS — Introduction © O. Nierstrasz 3
- 4. CSC141 Introduction to Computer Programming Machine language (1GL) • The lowest level of language. • The language used to program the first-generation computers. • The instructions in 1GL are made of binary numbers, represented by 1s and 0s. • 1s and 0s correspond to the on and off states of electrical switches. • Suitable for the understanding of the machine but very much difficult to interpret and learn by the human programmer.
- 5. Machine Language(contd) • is not portable • runs only on specific type of computer • is made up of binary-coded instructions (strings of 0s and 1s) • is the language that can be directly used by the computer 5
- 6. CSC141 Introduction to Computer Programming Assembly language (2GL) • Low-level language that allows a programmer to use abbreviations or easily remembered words instead of numbers. • These Observations are called Mnemonics. These Mnemonic are Opcode and Operands For Example: ADD AX, BX MOV CX, AX INC CX Op-code; ADD, MOV, INC Operands AX, BX,CX
- 7. CSC141 Introduction to Computer Programming Assembly language (2GL) (contd) • Programmer can write instructions faster but it is still not an easy language to learn. • Drawback: The language is specific to a particular processor family and environment. (Machine Dependent Language) • Assembler – A program that translates the assembly language program into machine language.
- 8. High Level languages (3GL) • A High-Level Language is an English-like language. • It is a refinement of a second-generation programming language. • It allowed users to write in familiar notation, rather than numbers or abbreviations. • Most High-level languages are not Machine Dependent. • Translator for High-level languages is either a Compiler or an Interpreter. • Examples of High-level languages: ―FORTRON ―COBOL ―BASIC ―C and C++ CSC141 Introduction to Computer Programming
- 9. High Level Languages (contd) • are portable • user writes program in language similar to natural language • examples -- FORTRAN, COBOL, Pascal, Ada, Modula-2, C++, Java • most are standardized by ISO/ANSI to provide an official description of the language 9
- 10. CSC141 Introduction to Computer Programming Very-High-Level Languages (4GL) • 4GLs are much more user-oriented and allow programmers to develop programs with fewer commands compared with 3GLs. • Non-Procedural Language; Programmers don’t have to specify all the programming logic, only tell the computer what they want done. • Saves a lot of time. • 4GLs consist of report generators, query languages, application generators, and interactive database management system • For example: • RPG III (Report Generator) • SQL (Structured Query Language) • NOMAD and FOCUS (DBMS)
- 11. Domain specific languages(DSL) • Specialized to a particular application domain. • Contrast to a general-purpose language (GPL), which is broadly applicable across domains, and lacks specialized features for a particular domain. • Wide variety of DSLs, ranging from widely used languages for common domains. • Sometimes informally called mini-languages. • Example: HTML for web pages.
- 12. CSC141 Introduction to Computer Programming Natural Languages (5GL) • Two types • Ordinary Human Languages; like English. • Programming language that use human language to give people a more natural connection with computers. • 5GLs are designed to make the computer solve a given problem without the programmer. • Natural languages are part of the field of study known as Artificial Intelligence. • Develop machines to emulate human-like qualities such as learning, reasoning, communicating, seeing and hearing.
- 13. What is Computer Programming? • It is the process of planning a sequence of steps (called instructions) for a computer to follow. 13 STEP 1 STEP 2 STEP 3 . . .
- 14. Problem Solving How do you solve problems? Understand the problem Devise a plan Carry out the plan Look back 14
- 15. Strategies Ask questions! • What do I know about the problem? • What is the information that I have to process in order the find the solution? • What does the solution look like? • What sort of special cases exist? • How will I recognize that I have found the solution? 15
- 16. Strategies Ask questions! Never reinvent the wheel! Similar problems come up again and again in different guises A good programmer recognizes a task or subtask that has been solved before and plugs in the solution Can you think of two similar problems? 16
- 17. Strategies Divide and Conquer! Break up a large problem into smaller units and solve each smaller problem • Applies the concept of abstraction • The divide-and-conquer approach can be applied over and over again until each subtask is manageable 17
- 18. Algorithms Algorithm A set of unambiguous instructions for solving a problem or subproblem in a finite amount of time using a finite amount of data Why must instructions be unambiguous? Why must time and data be finite? 18
- 19. Computer Problem-Solving 19 Analysis and Specification Phase Analyze Specification Algorithm Development Phase Develop algorithm Test algorithm Implementation Phase Code algorithm Test algorithm Maintenance Phase Use Maintain Can you name a recurring theme?
- 20. Phase Interactions 20 Should we add another arrow? (What happens if the problem is revised?)
- 21. A Tempting Shortcut? 21 GOAL THINKING CODE REVISE REVISE REVISE DEBUG DEBUG DEBUG TEST CODE
- 22. Developing an Algorithm Two methodologies used to develop computer solutions to a problem • Top-down design focuses on the tasks to be done • Object-oriented design focuses on the data involved in the solution But first, let's look at a way to express algorithms: pseudocode 22
- 23. An Algorithm is . . . • a step-by-step procedure for solving a problem in a finite amount of time. 23
- 24. Pseudocode Pseudocode A way of expressing algorithms that uses a mixture of English phrases and indention to make the steps in the solution explicit There are no grammar rules in pseudocode Pseudocode is not case sensitive 24
- 25. Example of algorithm • In this example, we design an algorithm to find the perimeter and area of a rectangle. • To find the perimeter and area of a rectangle, you need to know the rectangle’s length and width. • The perimeter and area of the rectangle are then given by the following formulas: • perimeter = 2 * (length + width) • area = length * width
- 26. The algorithm to find the perimeter and area of the rectangle is: 1. Get the length of the rectangle. 2. Get the width of the rectangle. 3. Find the perimeter using the following equation: perimeter = 2 * (length + width) 4. Find the area using the following equation: area = length * width
- 27. Problem-Solving Phase • ANALYZE the problem and SPECIFY what the solution must do • develop a GENERAL SOLUTION (ALGORITHM) to solve the problem • VERIFY that your solution really solves the problem 27
- 28. Implementation Phase: Program • translating your algorithm into a programming language is called CODING • with C++, you use Documentation -- your written comments Compiler -- translates your program into machine language Main Program -- may call subalgorithms 28
- 29. Implementation Phase: Test • TESTING your program means running (executing) your program on the computer, to see if it produces correct results • if it does not, then you must find out what is wrong with your program or algorithm and fix it--this is called debugging 29
- 30. Maintenance Phase • USE and MODIFY the program to meet changing requirements or correct errors that show up in using it • maintenance begins when your program is put into use and accounts for the majority of effort on most programs 30
- 31. Some C++ History • 1972 : Dennis Ritchie at Bell Labs designs C and 90% of UNIX is then written in C • Late 70’s : OOP becomes popular • Bjarne Stroustrup at Bell Labs adds features to C to form “C with Classes” • 1983 : Name C++ first used • 1998 : ISO/ANSI standardization of C++ 31
- 32. Three C++ Program Stages 32 myprog.cpp myprog.obj myprog.exe SOURCE OBJECT EXECUTABLE other code from libraries, etc. written in machine language written in machine language written in C++ via compiler via linker
- 33. Basic Control Structures • a sequence is a series of statements that execute one after another • selection (branch) is used to execute different statements depending on certain conditions • Looping (repetition) is used to repeat statements while certain conditions are met. • a subprogram is used to break the program into smaller units 33
- 34. SEQUENCE 34 Statement Statement Statement . . .
- 35. SELECTION (branch) 35 IF Condition THEN Statement1 ELSE Statement2 Statement1 Statement Condition . . . Statement2
- 36. LOOP (repetition) 36 WHILE Condition DO Statement1 Statement Condition . . . False
- 37. SUBPROGRAM (function) 37 SUBPROGRAM1 . . . SUBPROGRAM1 a meaningful collection of SEQUENCE, SELECTION, LOOP, SUBPROGRAM
- 38. Computer Components Central Processing Unit ( CPU ) 38 Control Unit Arithmetic Logic Unit Peripherals Auxiliary Storage Device Memory Unit ( RAM & Registers ) Input Device Output Device
- 39. Memory Organization • two circuit states correspond to 0 and 1 • bit (short for binary digit) refers to a single 0 or 1. Bit patterns represent both the computer instructions and computer data • 1 byte = 8 bits • 1 KB = 1024 bytes • 1 MB = 1024 x 1024 = 1,048,576 bytes 39
- 40. How Many Possible Digits? • binary (base 2) numbers use 2 digits: JUST 0 and 1 • decimal (base 10) numbers use 10 digits: 0 THROUGH 9 40