Operating System CSCI 125 & 161 / ENGR 144 Program that acts - - PDF document

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CSCI 125 & 161 / ENGR 144 Lecture 3

Martin van Bommel

Operating System

• Program that acts as interface to other

software and the underlying hardware

Operating System Utilities Compilers Utility Programs Assemblers Editors Hardware E-mail

HLL to Machine Language

• Enter HLL program into file using editor

– program.cpp - source file

• Translate source code to machine code - compiler

– program.obj - object file

• Combine object code with libraries - linker

– program.exe - executable file

• Move program to memory - loader

IDE

• Integrated Development Environment

– combines editor, compiler, linker, loader – usually includes tools to assist in debugging

• Note

– IDE’s do not always write to disk automatically – must remember to save work to disk often, especially before executing a program

Programming Errors

• Vocabulary and grammar - syntax
• Rules determine if statement legally

constructed - syntax rules

• Compiler checks rules - gives syntax errors
• Programs also contain errors in logic - bugs
• Debugging - finding & fixing logic errors
• e.g. 1962 Mariner I Venus probe crashed due to missing hyphen (-)

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Initial Program

#include <iostream> using namespace std; void main() { cout << ”Hello world!”; }

• library inclusion
• symbol namespace
• function “main”
• call function “cout”

to display string

Program Development

• Software Engineering
• study and use of techniques for

programming and problem solving

• Software Life Cycle
• software development goes through cycles,

where begins again when software outdated

Software Life Cycle

• 1. Specify the problem requirements.
• 2. Analyze the problem.
• 3. Design the algorithm to solve the problem.
• 4. Implement the program.
• 5. Test and verify the completed program.
• 6. Maintain and update the program.

Problem Analysis and Spec.

• Determine its input

– what information is given – what items are important to solving problem

• Determine its output

– what information must be produced to solve the problem

• Determine scope of the problem

– questions, questions, and more questions

Algorithm Design

• Procedure to convert inputs to outputs
• Uses step-by-step process
• Top-down step-wise refinement
• Produce pseudo-code or flowchart

Algorithm

• Three basic forms of control
• 1. Sequential - one step after another
• 2. Selection - choose one of many alternatives
• 3. Repetition - one or more steps repeatedly

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START GET NUMBER ADD NUMBER 10 NUMBERS? DIVIDE BY 10 PRINT RESULT END

YES NO

Program Coding

• Program should be correct, readable, and

understandable

• Simple and clear - no tricks
• Modular - program and test subtasks of
• verall problem separately
• Conforms to syntax of language

Program Formatting

• Spaces between items in statements

– between variables and operators

• Blank lines between major sections

– each subpart separated from others

• Good indentation

– indent statements in loops

• Meaningful variable names

– Distance and Time instead of d and t

Execution and Testing

• Test each unit separately before combining
• Use expected data with known result
• Use unexpected data to check for problems
• Validation - tested with several sets of test

data, but never can tell if absolutely valid.

Program Maintenance

• Programs survive for many years
• New features must be added
• Laws, rules, and procedures change
• Hardware changes
• e.g. Year 2000 problem