CSCI 125

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CSCI 125 161 / ENGR 144 Lecture 3

• Martin van Bommel

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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

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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

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IDE

• Integrated Development Environment
• combines editor, compiler, linker, loader
• usually includes tools to assist in debugging
• Note
• IDEs do not always write to disk automatically
• must remember to save work to disk often,
  especially before executing a program

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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 ltiostreamgt
• using namespace std
• int main()
• cout ltlt Hello world!
• return 0

• - library inclusion
• symbol namespace
• function main
• call function cout to display string
• - expected value to OS

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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  begins again when software outdated

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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.

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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

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Algorithm Design

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

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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?
NO
YES
DIVIDE BY 10
PRINT RESULT
END
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Program Coding

• Program should be correct, readable, and
  understandable
• Simple and clear - no tricks
• Modular - program and test subtasks of overall
  problem separately
• Conforms to syntax of language

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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

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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.

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Program Maintenance

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