CS208 Software Programming

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CS208 Software Programming

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Introduction

• Software
• Instructions that tell the computer what to do
  (ie. a program)
• Instructions are written in a programming
  language

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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

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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

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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 - scientific/engineering, math
• COBOL - business
• BASIC - education and PCs
• Pascal - education
• C/C - application development
• Java - 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

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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)
• Typed into the editor by the programmer using a
  programming language
• Object Code (object file)
• 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
High-Level Language Program Development
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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