int main()
{
int temp;
int *t;
int a=100,b=200;
//Using 3 variables
//1.1
temp = a;
a = b;
b = temp;
printf(“%d %d\n”,a,b);
//1.2
swap(&a,&b);
printf(“%d %d\n”,a,b);

//Using 2 variables
//2.1
a += b;
b = a-b;
a = a-b;
printf(“%d %d\n”,a,b);
//2.2
if(a!=0 && b!=0)
{
a *= b;
b = a/b;
a = a/b;
printf(“%d %d\n”,a,b);
}
//2.3
a = a^b;
b = a^b;
a = a^b;
printf(“%d %d\n”,a,b);
//Using 2 variables in single step
//3.1
a = b+a-(b=a);
printf(“%d %d\n”,a,b);
//3.2
a = b*a/(b=a);
printf(“%d %d\n”,a,b);
//3.3
a ^=b^=a^=b;
printf(“%d %d\n”,a,b);
return 0;
}
void swap(int *x,int *y)
{
int tmp;
tmp = *x;
*x = *y;
*y = tmp;
}

Line 2 :-
*7. int main(  -> error: expected declaration specifiers or ‘…’ before ‘{’ token
*8. int main   -> error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘{’ token
*9. in main()  -> error: unknown type name ‘in’
*10. int main(*) -> error: expected declaration specifiers or ‘…’ before ‘*’ token
*11. int main(‘) ->  error: missing terminating ‘ character
*12. If no main() -> error: expected identifier or ‘(’ before ‘{’ token

Line 3 :-
*13. if no {  -> error: expected declaration specifiers before ‘printf’
error: expected declaration specifiers before ‘return’
error: expected declaration specifiers before ‘}’ token
*14. ..{  -> error: expected ‘{’ at end of input
*15. {..  -> error: expected expression before ‘.’ token

Line 4 :-
*16. printf(“Hello World”). -> error: expected identifier before ‘return’
*17. printf(“Hello World”) -> error: expected ; before ‘return’
*18. printf(“Hello World”) -> error: expected ‘)’ before ‘;’ token
error: expected ‘;’ before ‘}’ token
*19. print(“Hello World”)  -> undefined reference to `print’
*20. print(Hello World)  -> error: ‘Hello’ undeclared (first use in this function)
*21. print(“Hello World)  -> warning: missing terminating ” character [enabled by default]
error: missing terminating ” character
error: expected expression before ‘return’
error: expected ‘;’ before ‘}’ token
Line 5 :-
*22. return c; -> error: ‘c’ undeclared (first use in this function)
Line 6 :-
*23. missing } -> error: expected declaration or statement at end of inpu

*/

/* Warnings

w1. If u remove header -> warning: incompatible implicit declaration of built-in function ‘printf’
*w2. #include<stdio.h> -> warning: extra tokens at end of #include directive [enabled by default]
*w3. return NULL       -> warning: return makes integer from pointer without a cast

*/ Special Case :-
/* ; -> You can freely put ; or ;; anywhere in main (before fn., after fn., blank line etc.)
*      Except you can’t put ; after main();
*      ;int main() -> Valid
*      {; ->         Valid
*      }; ->         Valid
*      printf(“Hello World”);; -> Valid
*    Shows warning if used after #include<stdio.h>;
*/

This is the most common type of device driver and there are plenty of simple examples in the source tree.

Character device drivers may transfer data between a user-level process and the device using any scheme other than the system buffer cache.

Character drivers control devices such as :-

——————————————

* network cards

* terminal devices

* printers

* specialized devices such as robots

* medical devices

* retail sales devices.

- In fedora for long lsting use command :

ll

- Linux does not use drive letters in pathnames like windows.
- Linux stores files within a single directory structure, called a virtual directory.
- Virtual directory contains filepaths from all storage devices installed on PC, mergedinto a single directory.
- There is a single base directory, called the root.
- root drive contains core of virtual directory.
- On root drive, Linux has special directories called mount points.
-When we start a new shell prompt, your session starts in your home directory.

i) man pages – These are manual pages .
- It contains interface to online reference manuals
- Press q to exit.
- How to Use ( Command ) – man command_name
- for all man pages of BASH shell, use
man bash
- It generally contains following information about command(command_name) :-
* Name
* Synopsis (Prototype)
* Description (Options)
* Author (author of command)
* Reporting Bugs (Feedback emails/Website)
* Copyright (copyright details)
* See Also (for further reference of command)

ii) Info pages – Read info documents
- It contains BASH manuals.
- Press q to exit
- How to Use (command) – info command_name
- It contains information about :-
* Prototype
* Introduction
* Options
* Exit Status
iii) help command
- It gives basic help for using a command and its various options.
- It gives output on Standard Output.
- It do not require exit command.
- How to Use (command) – help command_name
- It contains following information about command (command_name) :-
* Function of command
* Options
* Exit status

eg.
man echo
info echo
help echo

- To check total no. of enteries in each of three
I) type either of three (with space at end)
II) Press tab button for 3-4 times.
We will get the total number of possible options defined or list of them also.
eg. (<tab> means Press tab button)
man <tab><tab><tab>

BASH Shell Prompt Characters :-
Character Description
\a Bell Character
\d Date in format “Day Month Date”
\e ASCII escape character
\h Local hostname
\H Fully qualified domain hostname
\j Number of jobs currently managed by the shell
\l Basename of the shell’s terminal device name
\n ASCII newline character
\r ASCII carriage return
\s Name of the shell
\t Current time in 24-hour HH:MM:SS format
\T Current time in 12-hour HH:MM:SS format
\@ Current time in 12-hour am/pm format
\u Username of current user
\v Version of BASH shell
\V Release level of bash shell
\w Current working directory
\W Basename of current working directory
\# Command number of this command
\$ A dollar sign if normal user, #(Pound) for root user
/nnn Character corresponding to value nnn
\\ Backslash
\[ Begins a control code sequence
/] Ends a control code sequence

eg.
[ankur@(none) ~]$ PS1 = “[\t][\u]$”
[15:20:30][ankur]$

- Shell uses default PS1 prompt for initial data entry into shell.
- If we enter a command that requires additional information, shell displays second-tier prompt specified by PS2 .
- To display current settings for prompt use command :
echo $PS1
echo $PS2
- PS3 is used only in shell scripts.

- To change run level use init command

init run_level
- Most normal is run level 5 for graphical linux system.
- Level 1 is used for troubleshooting or emergency purpose.
- Most linux softwares start the network softwares at run level 3.
- What aplications work at Run level is determined by system by RC script.

There are 6 tasks in a socket :-
1. Create Socket.
2. Give name to socket.
3. Listen to socket for incoming connection.
4. Coonect the client to server.
5. Accept the request by server from client.
6. Close the socket

#include <stdio.h>

char *fgets(char *s, int size, FILE *stream);

Defination :-

fgets() reads in at most one less than size characters from stream and stores them into the buffer pointed to by s.  Reading  stops  after an EOF or a newline.  If a newline is read, it is stored into the buffer.  A terminating null byte (”) is stored after the last charac?
ter in the buffer.
Use :-

It is used to scan a string with spaces until a new line character or EOF character is inserted.

It takes input until enter is pressed.

It is used in place of scanf();

printf(“Enter no.of elements you want to sort:\t”);
scanf(“%d”,&N);//Max. no. of elements
printf(“Enter %d elements you want to sort:\n”,N);
for(i=0;i<N;i++)
scanf(“%d”,(a+i));
printf(“\nBefore sorting:\t”);
display(a,N);
//Sorting Starts
bubblesort(a,N);
//Sorting Ends
printf(“\nAfter sorting:\t”);
display(a,N);
}

int * bubblesort(int *a,int N)
{
int i,j,temp;
for(i=0;i<N-1;i++)
for(j=0;j<N-i-1;j++)
if(a[j]>a[j+1])
{
temp = a[j];
a[j]=a[j+1];
a[j+1]=temp;
}
return a;

}
int display(int* a,int N)
{
int i;
for(i=0;i<N;i++)
printf(“%d\t”,*(a+i));

return 0;
}