Chapter Ten

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Chapter Ten

• Developing UNIX Applications
• In C and C

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Lesson A

• C Language Programming

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Objectives

• Create simple C programs
• Debug C programs
• Use the make utility to revise and maintain
  source files
• Identify program errors and fix them
• Create a simple C programming application

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Introducing C Programming

• C is the language in which UNIX was developed and
  refined
• C programming may be described as a language that
  uses relatively short, isolated functions to
  break down large complex tasks into small and
  easily resolved subtasks
• This function-oriented design allows programmers
  to create their own program functions to interact
  with the predefined system functions to create
  powerful and comprehensive solutions to
  applications

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Creating a C Program

• A C program consists of separate bodies of code
  known as functions
• When these functions are put together in a
  collection, they become a program
• Within the program, the functions call each other
  as needed and work to solve the problem for which
  the program was originally designed

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Creating a C Program
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Creating a C Program

• The C library consist of functions that perform
  file, screen, and keyboard operations and when
  you need to perform one of these operations, you
  place a function call to it
• In terms of program format, every C function must
  have a name, and every C program must have a
  function called main
• To include comments in a C program, begin the
  comment line with / and end the comment with /

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Creating a C Program
Using the preprocessor include directive allowed
for the output shown here
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Creating a C Program
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Creating a C Program
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Creating a C Program

• Characters are represented internally in a single
  byte of computer memory, and when representing
  data in a program as a character constant,
  enclose it in singe quotes
• A string is a group of characters, like a name,
  which are stored in memory in consecutive
  locations, and when used as constants in a
  program, must be enclosed in double quotes

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Creating a C Program

• Identifiers are meaningful names given to
  variables and functions
• Variables must be declared before using them in a
  program, and declarations begin with a data type
  followed by one or more variable names
• The scope of a variable is the part of the
  program in which the variable is defined if
  this is done in a function, it is an automatic
  variable and if done outside a function, it is an
  external or global variable

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Creating a C Program
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Generating Formatted Outputwith printf
The output of a simple C program
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if Statements and C Loops

• C programs can use if statements to allow the
  program to make decisions depending on whether a
  condition is true or false
• C provides three looping mechanisms the for
  loop, the while loop, and the do-while loop

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if Statements and C Loops
The C loop generated the output here
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Defining Functions

• When a function is defined, its name is declared
  and its statements are written
• If a function is to return a value to the code
  that called it, the data type of the return value
  must be declared, too
• Sometimes it is necessary to pass data to a
  function and this data is called an argument

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Defining Functions
This function received an argument and returned a
value as a result of processing the argument
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Working with Files in C

• Files are continuous streams of data and they are
  typically stored on disk
• File pointers point to predefined structures that
  contain information about the file
• Before using a file, it must be opened
• The library function for this is fopen
• When done with a file, it must be closed
• The library function for this is fclose

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Working with Files in C

• File input and output (I/O) is performed with
  many functions in C
• fgetc performs character input
• fputc performs character output
• During an input operation, it is essential to
  test for the end of a file
• feof tests for the end-of-file marker

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Using the Make Utility toMaintain Program Source
Files

• Some programs have many files of source code
  which must be compiled and linked together
• Once compiled, the separate object files are
  linked together into the executable code

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Using the Make Utility toMaintain Program Source
Files
Two files were compiled and linked to form this
source code
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Using the Make Utility toMaintain Program Source
Files

• These multimodule source files can become quite
  difficult to maintain, especially when only a
  subset of the files are updated and need
  compiling
• This is where the make utility helps in that it
  tracks what needs to be recompiled by using the
  time stamp field for each source file
• All that is necessary is a control file, called
  the makefile, which lists the source files and
  their relationship to each other

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Using the Make Utility toMaintain Program Source
Files
The make utility helped in generating the program
seen here
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Using the Make Utility toMaintain Program Source
Files
The make utility helped in creating this
multimodule program
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Debugging Your Program

• There are many opportunities to make errors in
  your C programs and the compiler will identify
  errors made
• Common errors include incorrect syntax, missing
  semicolons, case-sensitive errors
• To correct syntax errors, follow these steps
• Write down the line number and a brief
  description
• Edit the source file
• Save and recompile the file

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Creating a C Program to Accept Input

• Use the scanf function to accept input from the
  keyboard
• scanf uses a control string with format specified
  in a manner similar to printf
• scanf can accept multiple inputs, but keep in
  mind that this usage can lead to difficult and
  cumbersome code

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Creating a C Program to Accept Input
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Creating a C Program to Accept Input
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Creating a C Program toAccept Input
An example of using C to accept keyboard input
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Encoding and Decoding Programs
Use the make command to help with encoding and
decoding
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Encoding and Decoding Programs
This program requests the name of the file to
encode
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Encoding and Decoding Programs
The files contents are encoded, which is what
happens when you encrypt a file
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Encoding and Decoding Programs
Once files are encoded, or encrypted, they can be
decoded or decrypted
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Lesson B

• C Programming in a
• UNIX Environment

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Objectives

• Create a C program that displays information on
  the screen
• Create a C program to read a text file
• Create a C program with overload functions
• Create a C program that creates a new class
  object

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Introducing C Programming

• C is a programming language that builds on C to
  add object-oriented capabilities
• C and C are similar in many ways
• C uses functions, as does C, but with added
  dimensions such as function overloading, which
  makes the functions respond to more than one set
  of criteria and conditions

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Introducing C Programming

• The major differences between C and C languages
  are
• C follows procedural principles, whereas C
  follows object-oriented principles
• C introduces a new data class called object,
  which is a collection of data and a set of
  operands called methods which manipulate the data

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Creating a C Program
Using C instead of C to create a program
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Creating a C Program That Reads a Text File
Using C instead of C to read text files
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How C Enhances C Functions
Function overloading allows C to take C
functions farther
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Setting Up a Class
A class data structure lets you create abstract
data types, such as a class for an object called
Cube
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Chapter Summary

• The C language concentrates on how best to create
  commands and expressions that can be elegantly
  formed from operators and operands
• C programs often consist of separate files called
  program modules that are compiled separately into
  object code and linked to other objects that make
  up the program
• The C program structure begins with the execution
  of instructions located inside a main function
  that calls other functions that contain more
  instructions

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Chapter Summary

• The make utility is used to maintain the
  applications source files
• The major difference between C and C is that C
  follows procedural principles and C primarily
  follows object-oriented programming
• The standard stream library used by C is
  iostream.h
• C provides two statements for standard input
  and output cin and cout respectively

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Chapter Summary

• C offers a way to define a function so that it
  can handle multiple sets of criteria this is
  called overloading
• endl skips a line like \n does in the C
  language
• You should use a class in C when your program
  performs specific operations on the data