CPS120: Introduction to Computer Science

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CPS120 Introduction to Computer Science

• Compiling Your First Program

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Compilers

• An engine that works on your behalf to process
  instructions and allow you to deal with various
  basic rules of the language
• The compilers job is to make sure you follow the
  rules, to require that you provide enough
  information that the compiler can translate you
  instructions into languages the components can
  understand

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Compilers Available

• Products range from freeware compilers to work
  environments designed for commercial application
  development
• Borland C compiler
• CodeWarrior
• IBM Visual Age C
• Microsoft Visual C
• GNU freeware
• DJGPP freeware (  www.delorie.com/djgpp/ )

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Compilation Process

1. Get the set of instructions from you (source
   file)
2. Review the instructions to see if they violate
   the rules (syntax) of the language
3. If all the rules are obeyed, create a working
   file in the language of the computer (machine
   language)
4. Attach to the working file full instructions for
   any shortcuts you may have used (linkage)
5. Assemble a final file in machine language
   (executable)

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Source Code

• The set of instruction that you will develop on
  your own for processing by the compiler

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Executable Files

• A machine-language executable file created when
  the compilation process is complete
• All that is needed to run the program
• Not human-readable
• Has the extension .EXE
• Stored in binary form
• Copies may be distributed (portable)
• Known as an application

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Compiling and Debugging

• Executable code will not be created until you
  correct all of the syntax errors in your source
  code
• Then the fun (with logic errors) begins

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Creating Source Code Files

• Actually Compiling a Program

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Creating Source Code

• Programmers spend most of their time with source
  code files
• Need to be comfortable with an editor that
  creates text files
• Dont use a word processor

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Using the Visual Studio Editor

• Save often because there is no autosave in Visual
  C
• The editor will do matching of delimiters and
  intelligent indentation

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Using C

• Actually Compiling a Program

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C Usages Conventions

• C is absolutely case sensitive
• For Instance A is 97 in ASCII and a is 65
• Remember in ASCII , , and ( are not equivalent
• No keywords in ANSI standard are even partially
  uppercase
• While is not a keyword, while is

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Comments

• Document what is happening, why it is happening
  and other issues
• Commentary is ignored by the compiler
• C has inline, block and documentary comments
• Inline comments are within line of code
• Use the // symbols
• Block comments are long comments delimited with
  / and /

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Scope Delimiters

• A symbol or pair of symbols used to define a
  region or area which is considered a locale
• In programming, many structures need to have
  their scope defined because they should not
  affect the entire program
• In C, the symbols and are used

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Literals

• Literals are system commands and other pieces of
  information that the compiler doesnt understand,
  and therefore, takes your word for them
• In C, literals are enclosed in straight double
  quotes " " which is the shift of the apostrophe

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Columns and White Space

• Modern programming languages are free form with
  delimiters instead of columns to determine the
  end of instructions
• The (semi-colon) is the delimiter used in C
• Use tabs, indents, and blank lines in any manner
  that makes code easier to understand
• Many programming instructions become subordinate
  to other instructions due to scope and other
  restrictions. Formatting code to reflect this
  makes it easier to read

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Variables

• Variables or identifiers are used to hold
  information
• Usually mixed case with the first letters small
  and the rest starting with a capital
• e.g. theWeight

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Color Coding in Visual C Editor

• Comments are green and are ignored by the
  compiler
• All ANSI keywords are coded in blue
• Other code is in plain black
• Compiler keywords like cin and cout are also
  shown in black

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Setting Up a Visual C Workspace

• Left-click START
• In the program section, select Visual Studio or
  Visual C (depending on what is installed)
• Left click on the Visual C icon to load the
  environment
• Create a new work area by choosing FILE/NEW
• Choose FILES tab
• Click on the C Source File to reach the editor
• Add a filename and directory before continuing
• e.g. c/cppFun/myFirstCpp

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Setting Up a Visual C Workspace

1. Create the directory with START / EXPLORE
2. Double-click the drive letter
3. Choose FILE, NEW FOLDER
4. Left click on FOLDER
5. Change new folder to cppFUN
6. Close Explorer with the X
7. Back in Visual C, type myFirstCpp in the file
   box
8. Click OK and get back to the main edit screen

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Setting Up a Visual C Workspace

1. Enter the source code
2. After entering the program, FILE then SAVE

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Why Create New Subdirectories?

• You should always use subdirectories to store
  your files. Visual C creates quite a few work
  files when it generates the executable file for
  you source code, and they will be easy to dispose
  of if you keep everything together in one
  convenient place.

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Running the Program

1. Press the REBUILD ALL button. It has two arrows
   in a box
2. Press the RUN button. It is a red exclamation
   point

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Disk Space Issues

• Text files are insignificant in terms of space
• However, at least six other files are created
  every time something is compiled
• Some of these are significantly larger
• You can delete anything but the file with the
  .cpp suffix everything else can be recreated
• You probably also want the .exe file

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An Introduction to Debugging

• CPS120
• Introduction to Computer Science
• Lecture 5

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Compiling and Debugging

• Executable code will not be created until you
  correct all of the syntax errors in your source
  code

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Syntax and Logic Errors

• A syntax error is simply the violation of the
  rules of a language misuse of structure and form
  in programming or a violation of the compilers
  rules. These errors are detected by the compiler
• Also know as 'fatal compilation errors'
• A logic error is a mistake that complies with the
  rules of the compiler that causes the program to
  generate incorrect output

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Linker Errors

• Not all syntax errors are detectable by the
  compiler
• These errors do not become apparent until files
  are put together to create an executable
• These errors are not linked to a specific line of
  code
• Look for the name of the variable and see what
  lines of code it occurs on using EDIT and FIND
• LNIK2001 unresolved external
• LNK1120 unresolved externals

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Debugging

• Debugging is the process of locating and fixing
  or bypassing bugs (errors) in computer program
  code or the engineering of a hardware device.
• To debug a program or hardware device is to start
  with a problem, isolate the source of the
  problem, and then fix it.

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Debugging Objective

1. Find the line(s) containing the syntax error(s)
   using the compiler's chosen line and error
   messages as a starting point

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Debugging is an Art

• Compilers often miss reporting an actual error
  and report on subsequent lines which are effected
  by error but may be completely correct
• After encountering a real syntax error, compilers
  often generate many incorrect syntax error
  messages
• Different compilers produce different errors and
  warnings for the same errors in the same program

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Debugging Steps

• Proofread before compiling
• Compile
• Correct all the obvious errors
• Start at the beginning of the list of errors and
  warnings
• A single syntax error may cause the compiler to
  believe numerous other syntax errors are
  occurring
• Look at the error lines and if you see the error,
  fix it. Otherwise, leave it for later. It may
  vanish when you fix something else
• Dont worry if more errors appear. Some errors
  mask other errors

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Debugging Steps

• Recompile when you have fixed what you recognize
• Repeat 3 4 until no further errors are obvious
• Attempt to solve the remaining errors in a
  top-down fashion
• Solve whatever errors you can without spending
  long periods of time on any given error
• Recompile whenever you feel you dont see any
  further solutions

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Debugging Aids

• In the Visual C (and other GUI-based compilers)
  double-clicking on an error message move the
  cursor to the line where the compiler detected
  the error
• This may not be the actual line where the error
  occurred dont trust the compiler on lines
• Work from the beginning of the program, because
  in most compilers, the errors are detected from
  the beginning to end, sequentially
• Some errors are so severe, they stop the compiler
  from continuing so more errors may appear after
  you successfully fix one or more

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A Debugging Mindset

• Assume your syntax is wrong. Look it up!
• Add working comments as you change things
• If you are 100 sure a line is correct, then
  search for a syntax error in the lines ABOVE that
  line
• Start with the immediately previous line and work
  backward
• Never make a change you cant explain

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Sample Debugging Comment

• cuot ltlt "This is a line of code"ltlt endl
• /Debug
• Error is undeclared identifier
• Checked syntax for endl
• Check syntax for screen output
• -- cuot is misspelled
• /

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Warnings

• Actions that may represent problems but do not
  cause the compiler to flag an error
• Dont ignore warnings
• Most common warning is a typecasting warning
• Indicates that the conversion of one type of a
  number was moved to a number (variable) of a
  different type without inclusion of a typecasting
  operation
• E.G. Moving a float to an integer variable

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Disk Space Issues

• If the floppy is full or becomes full during the
  compilation process, the compile will fail with
  an error message such as
• fatal error C1033 cannot open program database
• A very cryptic message like this can result
• If you are not able to view all of the
  intermediate files created in a compile, suspect
  a space error