CS208
Software Programming
7/11/2016
1
Introduction
Software

Instructions that tell the computer
what to do (ie. a program)

Instructions are written in a
programming language
2
Language Levels

Each type of CPU has its own specific
machine language

Other language levels were created to
make it easier for a human being to write
programs



machine language
assembly language
high-level language
3
Languages


Machine Language
 Zeros and Ones
 Bit representations are specific to a
particular hardware architecture
Assembly Languages
 Use mnemonics for operations and
sometimes also for memory locations
 Each assembly language is specific to a
particular hardware architecture
 Translated by an Assembler
4
Languages

High Level Languages –




Use English-like statements to instruct the
computer what to do
Are more portable (will run on different
kinds of hardware)
Are easier for humans to understand and
program with
Translated by a Compiler
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Programming Language
Capability Requirements

Representation & Storage (of both the Data and the
program Instructions)

Data Processing (Interprets the program instructions
and carries out the operations defined by these
instructions on the Data)

Data Input and Data Output

Input Data - data that is provided (is not computed)
to the program as it runs

Output Data - data that the program ultimately
produces (output data = solution of the
computational problem)
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Example Languages

High Level Languages






FORTRAN
COBOL
BASIC
Pascal
C/C++
Java
- scientific/engineering, math
- business
- education and PCs
- education
- application development
- application development
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Program Development

Program development consists
of:
 Discovering the underlying
algorithm
 Representing that algorithm as
a program using a
programming language
8
Programs


What is a program?

A collection of statements

Written in a programming language

Specify the steps taken to solve a problem
Each programming language has grammar
rules that specify:

How the statements are formed

How the statements are combined
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High-Level Language
Programming

Programming requires:

A programming language (e.g. C++) to
express your ideas

A set of tools to edit and debug your code

A compiler to translate your programs to
machine code

A machine to run the executable code on
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Types of Code

Source code (source file)


Object Code (object file)


Typed into the editor by the programmer using
a programming language
Translated from the source code by the
compiler
Executable Code

Created by the linker - links the object code
and any necessary library object code files
together
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Program Development
Computational Problem
develop
An Algorithm
encode
Source code Program in a High-Level Language
(e.g. C++)
Source
Code
High-Level
Language
Program
Development
Compiler
Linker
Object
Code
A machine Language
Program
12
Creating Computer Programs






Analyze the problem
Plan an algorithm
Hand check the algorithm
Code the algorithm (or write program)
Hand check (trace through) the
program
Evaluate and modify program as
necessary
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Structured Programming


Structured Programming is a technique used
to create well-formed programs
Uses top-down design with stepwise
refinement


Larger pieces of code are broken into shorter
pieces of code that encompass a single task
Task are repeatedly broken down into smaller
tasks, until they are small enough to be
understood easily
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Structured Programming
Concepts
 Final program is created via top-down design.
 Main code starts with empty modules, and is slowly
refined to lowest level
 Program is subdivided into modules (one
logical task, generally no more than one page
long)
 Keeps programmer from being overwhelmed by the
size of the job
 Allows easy division of work (modules assigned to
different programmers)
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Structured Programming
Concepts (continued)
 Each module is organized into recognizable
paragraphs, using indentation to show
nesting and subordinate clauses.
 Code structures should have only one entry
point and one point of exit (no GOTO).
 Embedded comments describe the function of
each data item and purpose of each module.
 Straightforward, easily readable code is
preferred over slightly more efficient, but
obtuse, code.
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Benefits of Structured
Programming
 More readable
 Easier to maintain
 More flexible
 More likely to be correct on first run
 Easier to "prove" by systematic program
verification
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