/boot: This directory contains everything required for the boot process except for configuration files not needed at boot time and the map installer.Thus, the /boot directory stores data that is used before the kernel begins executing user?mode programs.

/dev : /dev is the location of special or device files.It is a very interesting directory that highlights one important aspect of the Linux filesystem ? everything is a file or a directory.
/etc: This is the nerve center of your system, it contains all system related configuration files in here or in its sub?directories. A “configuration file” is defined as a local file used to control the operation of a program; it must be static and cannot be an executable binary.

/home: Linux is a multi?user environment so each user is also assigned a specific directory that is accessible only to them and the system administrator. These are the user home directories, which can be found under’/home/$USER’ (~/).home directory contains personal configuration files, the so?called dot files. Personal configuration files are usually ‘hidden’, if we want to see them,we either have to turn on the appropriate option in our file manager or run ls with the ?a switch. If there is a
conflict between personal and system wide configuration files, the settings in the personal file will prevail.

/initrd: initrd provides the capability to load a RAM disk by the boot loader. This RAM disk can then be mounted as the root file system and programs can be run from it. Afterwards, a new root file system can be mounted from a different device. The previous root (from initrd) is then moved to a directory and can be subsequently unmounted.initrd is mainly designed to allow system startup to occur in two phases, where the kernel comes up with a minimum set of compiled?in drivers, and where additional modules are loaded from initrd.

/lib: The /lib directory contains kernel modules and those shared library images needed to boot the system and run the commands in the root filesystem, ie. by binaries in /bin and /sbin.Libraries are readily identifiable through their filename extension of *.

/media: This directory contains subdirectories which are used as mount points for removeable media such as floppy disks, cdroms and zip disks.The motivation for the creation of this directory has been that historically there have been a number of other different places used to mount removeable
media such as /cdrom, /mnt or /mnt/cdrom.

/mnt: This is a generic mount point under which you mount your filesystems or devices. Mounting is the process by which we make a filesystem available to the system. After mounting our files will be accessible under the mount?point. This directory usually contains mount points or sub?directories where we mount our floppy and our CD. we can also create additional mount?points here if we wish. Standard mount points would include /mnt/cdrom and /mnt/floppy. There is no limitation to creating a mount?point anywhere on our system. It should be noted that some distributions like Debian allocate /floppy and /cdrom as mount points while Redhat and Mandrake puts them in /mnt/floppy and /mnt/cdrom respectively.

/opt: This directory is reserved for all the software and add?on packages that are not part of the default installation. Any package to be installed here must locate its static files (ie. extra fonts, clipart, database files) must locate its static files in a separate /opt/’package’ or /opt/’provider’ directory tree.Generally, all data required to support a package on a system must be present within /opt/’package’, including files intended to be copied into /etc/opt/’package’ and /var/opt/’package’ as well as reserved directories in /opt.

/proc: /proc is very special in that it is also a virtual filesystem. It’s sometimes referred to as a process information pseudo?file system. It doesn’t contain ‘real’ files but runtime system information (e.g. system memory, devices mounted, hardware configuration, etc). For this reason it can be regarded as a control and information centre for the kernel. In fact, quite a lot of system utilities are simply calls to files in this directory.
For example,’lsmod’ is the same as ‘cat /proc/modules’ while ‘lspci’ is a synonym for ‘cat /proc/pci’.
By altering files located in this directory we can even read/change kernel parameters (sysctl) while the system is running.

/root: This is the home directory of the System Administrator, ‘root’. This may be somewhat confusing (‘root on root’) but in former days, ‘/’ was root’s home directory (hence the name of the Administrator account). To keep things tidier, ‘root’ got his own home directory.

/sbin: Linux discriminates between ‘normal’ executables and those used for system maintenance and/or
administrative tasks. The latter reside either here or ? the less important ones ? in /usr/sbin. Locally installed system administration programs should be placed into /usr/local/sbin. Programs executed after /usr is known to be mounted (when there are no problems) are generally placed into /usr/sbin. This directory contains binaries that are essential to the working of the system. These include system administration as well as maintenance and hardware configuration program.we may find lilo, fdisk,init, ifconfig, etc…. here.

/usr: /usr usually contains by far the largest share of data on a system. Hence, this is one of the most important directories in the system as it contains all the user binaries, their documentation, libraries, header files, etc…. X and its supporting libraries can be found here. User programs like telnet, ftp, etc…. are also placed here.

/var: Contains variable data like system logging files, mail and printer spool directories, and transient and temporary files. Some portions of /var are not shareable between different systems. For instance, /var/log, /var/lock, and /var/run. Other portions may be shared, notably /var/mail, /var/cache/man, /var/cache/fonts, and /var/spool/news.’/var’ contains variable data, i.e. files and
directories the system must be able to write to during operation, whereas /usr should only contain static data.

/srv: /srv contains site?specific data which is served by this system. This main purpose of specifying this is so that users may find the location of the data files for particular service, and so that services which require a single tree for readonly data, writable datand scripts can be reasonably placed. Data that is only of interest to a specific user should go in that users’
home directory.

/tmp: This directory contains mostly files that are required temporarily. Many programs use this to create lock files and for temporary storage of data. Many these files are important for currently running programs. and deleting them may result in a system crash. Usually it won’t contain more than a few KB anyway. On most systems, this directory is cleared out at boot or at shutdown by the local system

RCS file: req1.c,v
Working file: req1.c
head: 1.1
branch:
locks: strict
access list:
symbolic names:
keyword substitution: kv
total revisions: 1; selected revisions: 1
description:
this is the requesting program in which i am subtracting two values.
the value given by requesting is read by server.
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revision 1.1
date: 2014/05/13 06:52:47; author: priya; state: Exp;
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RCS file: server.c,v
Working file: server.c
head: 1.1
branch:
locks: strict
access list:
symbolic names:
keyword substitution: kv
total revisions: 1; selected revisions: 1
description:
this is program for server which accepts all the request sent by requesting client and forward the request to the processing client.
in this i have created two pipes for receiving and sending request respectively .
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revision 1.1
date: 2014/05/13 06:54:25; author: priya; state: Exp;
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=============================================================================

RCS file: proc.c,v
Working file: proc.c
head: 1.1
branch:
locks: strict
access list:
symbolic names:
keyword substitution: kv
total revisions: 1; selected revisions: 1
description:
this is the program for processing client in which i have added two values.
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revision 1.1
date: 2014/05/13 06:58:28; author: priya; state: Exp;
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=============================================================================

RCS file: proc1.c,v
Working file: proc1.c
head: 1.1
branch:
locks: strict
access list:
symbolic names:
keyword substitution: kv
total revisions: 1; selected revisions: 1
description:
this is the program for processing client in which i have subtracted two values.
in this processing of request sent by server is done.
—————————-
revision 1.1
date: 2014/05/13 07:00:10; author: priya; state: Exp;
Initial revision
=============================================================================

RCS file: main.c,v
Working file: main.c
head: 1.1
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total revisions: 1; selected revisions: 1
description:
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revision 1.1
date: 2014/03/29 11:06:26; author: root; state: Exp;
Initial revision

RCS file: llrev.c,v
Working file: llrev.c
head: 1.1
branch:
locks: strict
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keyword substitution: kv
total revisions: 1; selected revisions: 1
description:
this is the program of reversing link list using three pointer.
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revision 1.1
date: 2014/03/29 11:02:35; author: root; state: Exp;
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RCS file: llrev.c,v
Working file: llrev.c
head: 1.2
branch:
locks: strict
access list:
symbolic names:
keyword substitution: kv
total revisions: 2; selected revisions: 2
description:
this is the program of structure in which i have entered data and link each data to node.
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revision 1.2
date: 2014/03/28 10:31:36; author: root; state: Exp; lines: +74 -22
this is the program ofreversing the link list using three pointer.
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revision 1.1
date: 2014/03/28 08:07:54; author: root; state: Exp;
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============================================

Calling a Function:

The call to a function in C simply entails referencing its name with the appropriate arguments. The C compiler checks for compatibility between the arguments in the calling sequence and the definition of the function.

Library functions are generally not available to us in source form. Argument type checking is accomplished through the use of header files (like stdio.h) which contain all the necessary information. For example, as we saw earlier, in order to use the standard mathematical library you must include math.h via the statement

Command-line arguments:

It is standard practice in UNIX for information to be passed from the command line directly into a program through the use of one or more command-line arguments, or switches. Switches are typically used to modify the behavior of a program, or to set the values of some internal parameters. You have already encountered several of these–for example, the “ls” command lists the files in your current directory, but when the switch -l is added, “ls -l” produces a so-called “long” listing instead. Similarly, “ls -l -a” produces a long listing, including “hidden” files, the command “tail -20″ prints out the last 20 lines of a file (instead of the default 10), and so on.

Conceptually, switches behave very much like arguments to functions within C, and they are passed to a C program from the operating system in precisely the same way as arguments are passed between functions. Up to now, the main() statements in our programs have had nothing between the parentheses. However, UNIX actually makes available to the program (whether the programmer chooses to use the information or not) two arguments to main: an array of character strings, conventionally called argv, and an integer, usually called argc, which specifies the number of strings in that array. The full statement of the first line of the program is

main(int argc, char** argv)

(The syntax char** argv declares argv to be a pointer to a pointer to a character, that is, a pointer to a character array (a character string)–in other words, an array of character strings. You could also write this as char* argv[]. Don’t worry too much about the details of the syntax, however–the use of the array will be made clearer below.)

Declaring Arrays:

Array variables are declared identically to variables of their data type, except that the variable name is followed by one pair of square [ ] brackets for each dimension of the array.
Uninitialized arrays must have the dimensions of their rows, columns, etc. listed within the square brackets.
Dimensions used when declaring arrays in C must be positive integral constants or constant expressions. ( Space is allocated only once, at the time the array is declared. The array does NOT change sizes later if the variable used to declare it changes. )

Examples:

int i, j, intArray[ 10 ], number;
float floatArray[ 1000 ];
int tableArray[ 3 ][ 5 ]; /* 3 rows by 5 columns

Initializing Arrays:

Arrays may be initialized when they are declared, just as any other variables.
Place the initialization data in curly {} braces following the equals sign. Note the use of commas in the examples below.
An array may be partially initialized, by providing fewer data items than the size of the array. The remaining array elements will be automatically initialized to zero.
If an array is to be completely initialized, the dimension of the array is not required. The compiler will automatically size the array to fit the initialized data.
Examples:

int i = 5, intArray[ 6 ] = { 1, 2, 3, 4, 5, 6 }, k;
float sum = 0.0f, floatArray[ 100 ] = { 1.0f, 5.0f, 20.0f };
double piFractions[ ] = { 3.141592654, 1.570796327, 0.785398163 };

Designated assignment:
This method can be mixed in with traditional iniitalization
For example:

int numbers[ 100 ] = { 1, 2, 3, [10] = 10, 11, 12, [60] = 50, [42] = 420 };

In this example,the first three elements are initialized to 1, 2, and 3 respectively.
Then element 10 ( the 11th element ) is initialized to 10
The next two elements ( 12th and 13th ) are initialized to 11 and 12 respectively.
Element number 60 ( the 61st ) is initialized to 50, and number 42 ( the 43rd ) to 420.
( Note that the designated initializers do not need to appear in order. )
As with traditional methods, all uninitialized values are set to zero.
If the size of the array is not given, then the largest initialized position determines the size of the array.

Using Arrays:

Elements of an array are accessed by specifying the index ( offset ) of the desired element within square [ ] brackets after the array name.
Array subscripts must be of integer type. ( int, long int, char, etc.
Arrays are commonly used in conjunction with loops, in order to perform the same calculations on all ( or some part ) of the data items in the array.

Sample Programs Using 1-D Arrays

The first sample program uses loops and arrays to calculate the first twenty Fibonacci numbers. Fibonacci numbers are used to determine the sample points used in certain optimization methods.

/* Program to calculate the first 20 Fibonacci numbers. */

#include
#include

int main( void ) {

int i, fibonacci[ 20 ];

fibonacci[ 0 ] = 0;
fibonacci[ 1 ] = 1;

for( i = 2; i < 20; i++ )
fibonacci[ i ] = fibonacci[ i - 2 ] + fibonacci[ i - 1 ];

for( i = 0; i < 20; i++ )
printf( "Fibonacci[ %d ] = %f\n", i, fibonacci[ i ] );

} /* End of sample program to calculate Fibonacci numbers */

Exercise: What is the output of the following program:

/* Sample Program Using Arrays */

#include
#include

int main( void ) {

int numbers[ 10 ];
int i, index = 2;

for( i = 0; i < 10; i++ )
numbers[ i ] = i * 10;

numbers[ 8 ] = 25;
numbers[ 5 ] = numbers[ 9 ] / 3;
numbers[ 4 ] += numbers[ 2 ] / numbers[ 1 ];
numbers[ index ] = 5;
++numbers[ index ];
numbers[ numbers[ index++ ] ] = 100;
numbers[ index ] = numbers[ numbers[ index + 1 ] / 7 ]–;

for( index = 0; index < 10; index++ )
printf( "numbers[ %d ] = %d\n" index, numbers[ index ] );

} /* End of second sample program

RCS file: string4.c,v
Working file: string4.c
head: 1.1
branch:
locks: strict
access list:
symbolic names:
keyword substitution: kv
total revisions: 1; selected revisions: 1
description:
this is the program to convert the contents in uppercase and write contents in output file.
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revision 1.1
date: 2014/03/20 03:59:05; author: root; state: Exp;
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1.1
date 2014.03.20.02.57.15; author root; state Exp;
branches;
next ;

desc
@this is the program in which i have first opened the file.
after opening the file , i have moved the file pointer to the last location using fseek function passing SEEK_END constant.
i have used ftell to know the position of file pointer .after that i have read last character from file.
@

1.1
log
@Initial revision

1.1
date 2014.03.20.02.00.48; author root; state Exp;
branches;
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desc
@this is the program to copy contents of one file into another using fputc.
@

1.1
log
@Initial revision
@
text
@#include
#include
int main()
{
FILE *fp, *fp1;
char ch,ch1;
fp=fopen(“/home/priya/pp1.c”,”r”);
fp1=fopen(“/home/priya/palak1.c”,”w”);
do
{
ch=fgetc(fp);
ch1=fputc(ch,fp1);

}
while(ch !=10);
// printf(” the string is ch is %c”,ch);
// printf(“the string is ch is %c”,ch1);
return 0;
}

@

RCS file: avgptr.c,v
Working file: avgptr.c
head: 1.1
branch:
locks: strict
access list:
symbolic names:
keyword substitution: kv
total revisions: 1; selected revisions: 1
description:
this is a program in which we have calculated the average of array elemsing pointer.
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revision 1.1
date: 2014/03/06 11:14:55; author: root; state: Exp;
Initial revision