Overview of Computer Programming

by eturo

Programming a computer is both a creative activity and a process structured by rules. Computers are programmed or given instruction, through the use of programming languages, so to program a computer, one must learn a programming language.

What is a computer program?

·         is a collection or set of directions that tell the computer exactly what to do;

·         it is the medium used to communicate with the computer;

·         can be written in many programming languages; and

·         they are designed and written by computer programmers

What is a programming language?

Learning a programming language has similarities to learning a natural language, such as English or Spanish or Japanese. Natural languages have a lexicon, a syntax, and a semantics. The lexicon is the vocabulary and punctuation. The rules of syntax dictate how the lexicon can be ordered to form correct sentences. The semantics conveys the meaning when the chosen words are combined in the chosen syntax of each sentence. The semantics changes, sometimes in subtle ways, depending on both the words chosen and the sentence syntax.

So too, a programming language has lexical elements, a syntax, and a semantics.

• Lexical elements – are comprised of keywords in the programming language, symbols such as arithmetic operators or parenthesis or braces, and words denoting identifiers by which we can name what is being operated upon
• Syntax – specifies precise rules for how the lexical elements are ordered to form correct language statements and programs
• Semantics – is the meaning of the constructed language statements

Therefore, a programming language are languages for specifying sequences of directions or instructions for the computer

Two Types of Programming Languages

1.       High - level languages

·         they allow specification of program instructions in a manner closer to natural languages, but without the ambiguity and lack of precision

·         rely on Graphical User Interface (GUI) featuring symbolic icons and drag-and-drop technique and uses English-like statement

·         software written on one computer could be used on another; programmers could work on different computers without having to learn a new assembly

·         e.g. C, C++, Java, Visual Basic, Visual Basic.Net. C#

2.       Low - level languages

·         it is only capable of executing exceedingly primitive instructions known as the machine language

·         uses mnemonic code / symbols

·         e.g. Assembly Language

Classification of Programming Languages

1.       Procedural - procedures are expressed as specific algorithms. Each procedure to be executed by the computer is written, one instruction at a time.

–  COBOL (Common Business Oriented Language), C, Fortran (Formula Translation), Pascal

2.      Functional - process steps are expressed by composition of basic functions (list processing.

–  Lisp ( list - processing language)

3.       Logic - relations are defined by basic logic formulas (inferential processing).

–  ProLog ( Programming for Logic)

4.      Object-Oriented - operation is conducted by objects which integrate the data and their processing.

–  Java, C++, Smalltalk

Language Translators

·         translates programs written in a variety of programming languages into machine language codes.

 Three Types of Language Translator:

1.       Compiler – a computer program that translates high level language into machine language at only one time. This is used mainly by high-level languages.

2.      Interpreter – a computer program that translates high level language into machine language one line at a time. This is used mainly by high-level languages.

3.       Assembler – a computer program that translates assembly language into machine language at only one time. This is used mainly by low-level languages.

Problem Solving through Programming

Programming is about solving problems. Regardless of the language used, this activity proceeds through a set of well-defined stages during the development of the program.

1. Some Tools in Problem Solving in Programming

·         Algorithm - sequence of steps in solving a problem; list of instructions for carrying out some process step by step

·         Pseudocode - English-like step-by-step description of the solution

·         Flowchart - a diagram representing the logical sequence which a combination of steps or operations is to be performed; consists of labeled geometrical symbols that are interconnected to provide a pictorial representation of a data processing procedure; visual representation of an algorithm

Symbols	Symbol Name and Definition
parallelogram	INPUT/OUTPUT represents an instruction to an input or an output device
rectangle	PROCESSING represents a group of program instructions that perform a processing function of the program
diamond	DECISION denotes point in the program where more than one path can be taken
hexagon	PREPARATION represents instructions that will alter, or modify a program’s course of execution (initialization)
oval	TERMINAL used designate the beginning and end of program, or a point of interruption
rectangle with 2 predefined vertical bars	PREDEFINED PROCESS represents a named operation or programmed step not explicitly detailed in the program flowchart; can be used when a procedure needs to be repeated several times
small circle	ON-PAGE CONNECTOR used to connect one part of a flowchart to another without drawing flow lines within same page
small pentagon	OFF-PAGE CONNECTOR used to designate entry to or exit from a page when it require more than one page
lines with arrowhead	FLOW LINES & DIRECTION INDICATORS used to show reading sequence in which flowchart symbols are to be read

2. Steps in Problem Solving through Programming

Design. In the design stage, a careful problem statement is articulated, indicating the desired outcomes of the program. The problem statement is then refined by listing a set of steps designed to accomplish the goal. The set of steps is called an algorithm, and may be presented in English or in some other appropriate notation. The design stage does not require the use of a computer.

Edit. In the edit stage, a program is created in a text editor and stored in one or more files on disk. These files are known as the program source code.

Compile. During the compile stage, the compiler translates the program source code in the source file(s) into the machine code appropriate for the machine on which the program will execute.

Execute. The execute stage is the time when the compiled program is loaded from disk into its execution environment and the machine carries out the instructions.