Page 118 - DCAP405_SOFTWARE_ENGINEERING

Unit 7: Software Engineering Practice

7.5.2 Coding Concepts Notes

Computer programs are collections of instructions that tell a computer how to interact with the
user, interact with the computer hardware and process data. The first programmable computers
required the programmers to write explicit instructions to directly manipulate the hardware of
the computer. This “machine language” was very tedious to write by hand since even simple
tasks such as printing some output on the screen require 10 or 20 machine language commands.
Machine language is often referred to as a “low level language” since the code directly
manipulates the hardware of the computer.
By contrast, higher level languages such as C, C++, Pascal, Cobol, Fortran, ADA and Java are
called “compiled languages”. In a compiled language, the programmer writes more general
instructions and a compiler (a special piece of software) automatically translates these high
level instructions into machine language. The machine language is then executed by the
computer. A large portion of software in use today is programmed in this fashion.
We can contrast compiled programming languages with interpreted programming languages.
In an interpreted programming language, the statements that the programmer writes are
interpreted as the program is running. This means they are translated into machine language on
the fly and then execute as the program is running. Some popular interpreted languages include
Basic, Visual Basic, Perl and shell scripting languages such as those found in the UNIX
environment.
We can make another comparison between two different models of programming. In structured
programming, blocks of programming statements (code) are executed one after another. Control
statements change which blocks of code are executed next.
In object oriented programming, data are contained in objects and are accessed using special
methods (blocks of code) specific to the type of object. There is no single “flow” of the program
as objects can freely interact with one another by passing messages.
In this tutorial, we focus only on structured programming.

Program Structure
Virtually all structured programs share a similar overall structure:

Statements to establish the start of the program
Variable declaration

Program statements (blocks of code)
The following is a simple example of a program written in several different programming
languages. We call this the “Hello World” example since all the program does is print “Hello
World” on the computer screen.

Notes The Perl and Basic languages are technically not compiled languages. These language
statements are “interpreted” as the program is running.

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