Chapter Ten
Developing UNIX
Applications
In C and C++
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 Output
with 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 to
Maintain 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 to
Maintain Program Source
Files
Two files were
compiled and
linked to form this
source code
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Using the Make Utility to
Maintain 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 to
Maintain Program Source Files
The make utility
helped in
generating the
program seen
here
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Using the Make Utility to
Maintain 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 to
Accept 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 file’s 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
application’s 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
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