computer pratices lab ii (ge 27)

8/6/2019 Computer Pratices Lab II (GE 27)

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COMPUTER PRATICES LAB II 201

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STUDY ON UNIX

Ex No: 1

AIM: To perform a study on UNIX

An operating system is the software component of the computer system that is responsible for

the management and coordination of activities and the sharing the limited resources effectively. The

figure 1 shows the layered structure of the system and where the operating system is located in it.

Fig 1. Layered Structure

Operating systems offer a number of services to application programs and users. Users may also

interact with the operating system with some kind of software user interface (UI) like typingcommands by using command line interface (CLI) or using a graphical user interface (GUI). For

hand-held and desktop computers, the user interface is generally considered part of the operating

system. On large multi-user systems like UNIX and Unix-like systems, the user interface is generally

implemented as an application program that runs outside the operating system.

There are basically two types of operating system.

1. Single user operating system

2. Multi user operating system

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In single user operating system only one person can use the system at the same time. The

examples are DOS, Windows 95 and Windows 98.In multi-user operating system more than one

person can use the system at the same time. The examples are UNIX, LINUX and WINDOWS NTetc.

The UNIX operating system is made up of two major parts, the kernel and the shell.

a) The kernel

The kernel of UNIX is the hub of the operating system: it allocates time and memory to programs andhandles the file store and communications in response to system calls. As an illustration of the waythat the shell and the kernel work together, suppose a user types rm myfile (which has the effect ofremoving the file myfile). The shell searches the filestore for the file containing the program rm, and

then requests the kernel, through system calls, to execute the program rm on myfile. When the processrm myfile has finished running, the shell then returns the UNIX prompt $ to the user, indicating that itis waiting for further commands.

b) The shell

The shell acts as an interface between the user and the kernel. When a user logs in, the login programchecks the username and password, and then starts another program called the shell. The shell is acommand line interpreter (CLI). It interprets the commands the user types in and arranges for them to

be carried out.

History - The shell keeps a list of the commands you have typed in. If you need to repeat a command,use the cursor keys to scroll up and down the list or type history for a list of previous commands.

THE DIRECTORY STRUCTURE

A file is a collection of information that is assigned a name that is used to identify the file. Files are

grouped under directory to avoid cluttering of files. A directory can have one or more directories in it

called subdirectories. In UNIX files and directories are arranged in a hierarchical manner. The top of

the hierarchy is traditionally called root.

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LOGGING IN AND LOGGING OUT

These are the security for the system with many users.

Logging into a UNIX system requires two information. They are

1. User name2. Password

Logging out is done if we want to quit. The command used for this is exit.

ADVANTAGES OF UNIX OPERATING SYSTEM

UNIX is more flexible and can be installed on many different types of machines,

including mainframe computers, supercomputers and microcomputers. UNIX is more stable and does not go down as often as Windows does, thereforerequires less administration and maintenance.

UNIX has greater built-in security and permissions features than Windows.

UNIX possesses much greater processing power than Windows.

RESULT:

Thus basic of UNIX was studied.

Ex.No:2 BASIC UNIX COMMANDS

AIM: To study the BASIC UNIX Commands.

1. Date command

The date command tells us the current date and time

Format: $date Eg:$date

The date command can also be used with the following format specification.

$date +%m : To display only month

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$date +%h : To display month name

$date +%y : To display last two digits of the year

$date +%H : To display Hours

$date +%M : To display Minutes

$date +%S : To display Seconds

2.who command

This command gives us the details of who all have logged into the UNIX system currently.

Format:$who Example: $who am I

This tells us to when we had logged in and the systems name for connection being used.

3.man command

This command prints manual page.

Format :$man Example:$man who

4.pwd command

It tells us the full path for the current directory

Format:$pwd

5.ls command

The ls command displays the list of files in the current directory.

Format :$ls

Various options for ls command

ls -l :List files in login format. The files are displayed along with their mode,

number of links, owner of files, file size, modification date &time and

file name.

ls -t : Lists in order of last modification time

ls a : List all entries, including hidden files.

ls d : Lists directory files instead of contents.

ls p : puts a slash after each directory.

ls u : Lists in order of last access time

6.mkdir command

This command helps us to make a directory.

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Format :$mkdir

Example:$mkdir abc

7.rmdir command

This command is used to remove a directory from the disk.

Format :$rmdir

Example:$rmdir abc

8.cd command

This command is used to move from one directory to another.

Format:$cd

Example:$cd abc

9.cat command

This command is used to create a file.

Format:$cat[path]filename

Example :$cat xyz

$cat>abc

Have a nice day

Ctrl d

10.cp command

This command helps us to create duplicate copies of ordinary files.

Format:$cp[path]source filename [path]destination filename

Example:$cp abc def

11.ln command

This command is used to establish an additional file name for the same ordinary file.

Format:$ln oldfilename newfilename

Example:$ln abc def

12.mv command

This command move a file from one place to another place.

Format :$mv source destination

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Example: $mv abc def

13.rm command

This command is used to remove one or more files from a directory. This can be used todelete all files as well as the directory.

Format: $rm[path]file

rm i asks the user if he wants to delete the files mentioned.

rm r recursively delete the entire contents of directory as well as the

directory itself

14.echo command

This command is used to display whatever message we want to display on the screen.

Format:$echomessage

Example:$echo learning UNIX is easy

15.grep command

The grep utility searches one or more files to see if any contain a specified string ofcharacters.

Format: grepstringfilename

Example:$grep lily flower

16.diff command

The diff utility compares two files and displays a list of the difference between them. Itdisplays the list of actions to be taken to convert one file into another.

Format: $diff filename1 filename2

Example:$diff flower1 flower2

17.read command

This command is used in shell scripts.this command waits for the user to input the value ofthe variable.

Format: $read variablename

18. clear/tput clear commands

The clear/tput clear utility clears the screen.

Format:$clear

$tput clear

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19.exit command

Press(ctrl+D) in response to the shell prompt to logout.

Format:$exit

Exercises:

1.Create the following directory structure in your home directory.

Oos

File1 file2 file3 File5

2..From the directory OS change to the directory to win95.

3.Display the content of this directory in various formats.

4.Copy the file1 to the folder LINUX.

5.Rename the file1 present in the directory LINUX to file4.

6.Copy the content of file4 to file5 in the same directory.

7.Set the permission of the file3 to read write execute for user,read execute for

group and read only for others.

8.Now clear the computer screen.

9.Then show the directory where you are.

10.Display the calendar for the year 2009.

7

OS

MUOSSUOS

DOS Win9 UNIX LINU


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11.Check the similarity between file1 and file3.

12.Change your password and again re-change to the original one.

13.Remove the whole directory structure.

RESULT:

Thus basic of UNIX Commands was studied.

Ex No:3 SHELL PROGRAMMING

A Linux shell is a command language interpreter, the primary purpose of which is to translate the

command lines typed at the terminal into system actions. The shell itself is a program, through which

other programs are invoked

What is a shell script ?

A shell script is a file containing a list of commands to be executed by the Linux shell. shellscript provides the ability to create your own customized Linux commands

Linux shell have sophisticated programming capabilities which makes shell script powerfulLinux tools

How to work with shell ?

Step1:

In the dollar prompt type

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$ vi < file name>

Where vi is the editor ,it will open a new window in which you can type the program you want

Step2:

After typing the program press ESC and : together then at the bottom of the vi screen you can see i.e.

prompt .In that type as wq which means write and quit i.e. the content what is typed will be written

and saved into that file that has been created

Step3:

Once wq is typed at the : prompt ,the prompt would change to $ symbol in which you have to do the

following

$ sh < file name >

Sh command is used to run the shell program

- is the name of the file for which the output is to be got

Basically to print a text in the your shell programs echo command is used

SYNTAX FOR LOOPING STATEMENTS

IF THEN-ELSE CONSTRUCT

if [ condition]

then

else

statements

fi (end of if)

WHILE

while

do

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Done

CASE

Case $ in

1) ;;2) ;;3) ..4).

*) ;;

esac

For loop

For(( intitialization;condition;incremetation/decrementation))

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Ex No 3.a Displaying wishes:

Aim: To write a shell program to display the wishes based on the time.

Algorithm:

1. Find the time2. Based on the time display the wishes as either good morning or good afternoon or good

evening or good night3. Display both time and wishes

4. Terminate the processProgram:

d=`date +%H`

echo $d

[ $d -gt 00 -a $d -lt 12 ] && echo "Good Morning"

[ $d -lt 16 -a $d -gt 12 ] && echo "Good Afternoon"

[ $d -gt 19 -a $d -lt 19 ] && echo "Good Evening"

[ $d -gt 19 -a $d -lt 23 ] && echo "Good Night"

Result:

Thus the time was found and a wish was displayed using the shell program.

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Ex no: 3b Biggest of two numbers:

Aim: To write a shell program to find the bigger of two numbers.

Algorithm:

Start the program

Read the 2 numbers a & b

Check whether a is greater than b. If true, display a is greater

Or display b is greater.

TerminateProgram:

echo enter the first no

read a

echo enter the second no

read b

if [ $a -gt $b ]

then echo the biggest no is $a

else echo the biggest no is $b

fi

Result:

Thus the bigger of 2 numbers was found using the shell program

ExNo3.c Biggest of three numbers

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Aim:

To write a shell program to find the biggest of three numbers.

Algorithm:

Start the program

Read the three numbers a, b, c

Check if a > b and a > c

If true, display a is greater

Or check if b > c

If true, display b is greater

Or display c is greater

TerminateProgram:

echo Enter the first number:

read a

echo Enter the second number:

read b

echo Enter the third number:

read cif [ $a -gt $b -a $a -gt $c ]

then

echo "$a is greater."

elif [ $b -gt $c ]

then

echo " $b is greater. "

else

echo "$c is greater."

fi

Result:Thus the biggest of 3 numbers was found using the shell program.

Ex No.3d String Comparison

Aim:

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To write a shell program for performing string comparison

Algorithm:

Start the program

Read the two strings

Check if they are equal

If true, display the strings are equal

Or display the strings are not equal

TerminateProgram;

echo enter string 1

read s1

echo enter string2

read s2

if [ $s1 == $s2 ]

then

echo the given string are equal

else

echo The given strings are not equal

fi

Result:

Thus two strings were compared using the shell program

Ex no 3e Arithmetic Operations

Aim: To write a shell program to perform arithmetic operations using switch statement

Algorithm:

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1. Enter the input2. Enter the choice

3. Perform corresponding arithmetic operation on the inputs4. Display the resultProgram:

echo "enter the first no:"

read a

echo "enter the second no:"

read b

echo "enter ur choice"

read n

case $n in

1) echo "addition" ;

c=èxpr $a + $b `;

echo "The sum is $c." ;

exit ;;

2) echo "subtraction" ;

c=èxpr $a - $b `;

echo "The difference is $c." ;

exit ;;

3) echo "multiplication" ;

c=èxpr $a \* $b `;

echo "The product is $c." ;

exit ;;

4) echo "division" ;

c=èxpr $a / $b `;

echo "The quotient is $c." ;

exit ;;

*) echo "Invalid" ;

esac;;

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Result:

Thus the arithmetic operations were performed using the shell program.

Ex No: 3f Sum of n even numbers

Aim:

To write a shell program for calculating the sum of n even numbers

Algorithm:

1. Read the value of n 2. Initialize the variables sum and i as zero3. Using while loop, increment the value if i by 2

4. Calculate the value of sum5. Display the result6. Terminate

Program:

echo -----------------------

echo Sum of 'n' even numbers

echo -----------------------

echo enter the value of n

read n

sum=0

i=2

while [ $i -le $n ]

do

sum=`expr $sum + $i`

i=`expr $i + 2`

done

echo The sum of even numbers upto $n is $sum

Result:Thus the sum of even numbers upto n was found using the shell program.

Ex No:3g SUM OF n NATURAL NUMBERS

Aim:

To write a shell program for calculating the sum of n natural numbers

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Algorithm:

Read the value of n Initialize the variables sum and i as zero

Using while loop, increment the value if i

Calculate the value of sum

Display the result

TerminateProgram:

echo --------------------------

echo Sum of 'n' natural numbers

echo --------------------------

echo Enter the value of n

read n

sum=0

i=0

while [ $i -le $n ]

do

sum=`expr $sum + $i`

i=`expr $i + 1`

done

echo The sum of first $n natural numbers is $sum

Result:

Thus the sum of n natural numbers was found using the shell program

Ex No: 3h Generation of Fibonacci Series

Aim: To write a shell program to generate Fibonacci series

Algorithm:

1. Initialize a and b with 0 and 1

2. Get the limit and initialize i with 0

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3. Initialize i4. Add a and b and assign to c

5. Print c6. Assign the value of b to a and the value of c to b7. Increment i by 18. Repeat the above steps until i is less than n

Program:

echo Gneration of fibonaaci series

a=0

b=1

c=0

echo "Enter the limit:"

read n

i=3

echo "FIBONACCI SERIES"

echo $a

echo $b

for((i=0;$i


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There are three basic modes of operations in VI.

a) Command modeb) Insertion modec) Last Line mode

A) Command Mode:

The command mode is one which user is able to enter commands. The command

mode allows the entry of commands to manipulate text. These commands are usually one or two

characters long, and can be entered with few keystrokes.

B) Insertion Mode:

The insertion mode is one in which, the user can enter the data or edit the data. The

insert mode puts anything typed on the keyboard into the current file.

C) Last Line Mode:

The Last line mode is one in which user is able to enter special commands.

STARTING VI EDITOR:

To start using vi, at the UNIX prompt type vi followed by a file name.

$vi newname

at the Unix $ prompt, where newname is the name you wish to give the new file. On the screen youwill see blank lines, each with a tilde at the left, and a line at the bottom giving the name and status of

the file:

~

~

"testvi" [New file]

Use vi to open an already existing file by typing vi filename where filename is the name of the

existing file. If the file is not in your current directory, you must use the full pathname.

ENTERING TEXT:

vi has two modes: command mode and insert mode. In command mode, the letters of the

keyboard perform editing functions (like moving the cursor, deleting text, and so on). In insert mode,

the letters you type form words and sentences. Unlike word processors, vi starts up in command

mode. To begin entering text in an empty file, you must change from command mode to insert mode.

To do this, type the letter i. You may see INSERT MODE at the bottom right of the screen, or nothing

may appear to change, but you are now in insert mode and can begin typing text. If you make a

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mistake, pressing the Backspace or Delete key may or may not remove the error, depending on the

configuration of the software you are using to connect to the Login Service.

ENDING THE EDIT SESSION:

While editing, VI keeps the edited text in an area called work buffer. When editing is

finished, the user must write out the contents of the work buffer to disk file.

Keeping VI in command mode,

1. The ZZ (upper case) command can be used to write the newly entered text to the disk andthen end the editing session and returns the control to the shell.

2. To exit without saving the work, use :q! command

3. To quit after writing change to the disk file :wq command is used

4. To quit after replacing the old copy of the file with the new one, :x command is used.

COMMANDS:

a) Getting out

When we want to get out of the editor, switch to command mode(press ESC) if necessary,

then

:q Quit vi

:q! Quit vi without saving changes

:w Save and continue working in vi

:wq Save the changes and exit from vi

:x Save and exit from vi

ZZ Save the changes and exit from vi

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b) Inserting Text

From command mode, these keystrokes switch you into insert mode with new text beinginserted.

i Invokes insert mode inserts before character

I Same as i but insertion is at beginning of line

o Opens blank line before current line

O Same as o but puts blank line after current line

a Same as i but appends after cursor

A Same as a but appends at end of line

c) Deleting Text

The following commands allow you to delete text

x Deletes one character at the cursor position

n x Delete the n ext n characters at the cursor position

dw Deletes one word at the cursor position

n dw Deletes n words at the cursor position

d0 Deletes from the cursor position till the beginning of the line

d$ Deletes from the cursor position till the end of the line

dd Deletes one line at the cursor position

n dd Deletes the next n lines from the cursor position

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d) Moving Around

When in command mode we can use the arrow keys to move the cursor up,down,left,right. Inaddition, these keystrokes will move the cursor:

k Same as the up arrow key

h Same as the left arrow key

l Same as the right arrow key

j Same as the down arrow key

w Moves forward by a word

nw Moves forward by n number of words

e Moves to the last character of this word or that of the next

ne Moves to the last character of n the next word

b Takes the user back by a word

n b Takes the user back by n number of words

0(zero) or

^

Takes the user to the beginning of the line

$ Takes the user to the end of the line

n G Takes the user to the n the line

L Takes the user to the last line

Cutting, Copying, Pasting:

From command mode, use these keystroke (or keystroke-combination) commands for the

described cut/copy/paste function:

yy Copy a line into temporary storage

nyy Copy n number of lines into temporary storage

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dd Move a line into temporary storage

ndd Move n lines into temporary storage

p Move the text from temporary storage into the current position of cursor

Searching for text:

Instead of using the moving around commands above, we can go directly forward or

backward to specified text using / and ?

/g Search for a pattern g forwards

?g Search for a pattern g backwards

/ Repeat the last search forward

? Repeat the last search backward

Replacing Text:

This amounts to combining two steps; deleting, then inserting text.

r Replace a single character at the current cursor position

R Invoke insert mode and go on replacing till is pressed

s Deletes the current character and inserts character until is pressed

S Removes all characters on the current line and allows the user to enter data

Undoing your changes:

u Undoing the previous changes

Screen Manipulation:

The following commands allow the vi editor to move up and down several lines and to be

refreshed

Ctrl-f Scrolls screen forward

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Ctrl-b Scrolls screen backward

Ctrl-u Scrolls half a screen backward

Ctrl-d Scrolls half a screen forward

Ctrl-L Refreshes the screen

Exercises

1. Create a file under the name vifile and enter the following text

An operating system is the software component of the computer system that is responsible for

the management and coordination of activities and the sharing the limited resources effectively.

2. Save the file

3. Append the following line at the bottom of current file

Operating system offers a number of services to application programs and users.

4. Move the cursor to the top of screen, bottom of screen and middle of screen

5. Search for the word system and enter the following lines below it.

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The kernel of UNIX is the hub of the operating system: it allocates time and memory to

programs and handles the file store and communications in response to system calls.

6. Search for the word software and replace it with hardware.

7. Go to the 3rd line

8. Delete the line

9. Undo the deletion

10. Copy the first three lines and paste it as 6 to 9 th line

11. Move the lines 2 to 4 to the bottom of the file

12. Search for the word is forward and in reverse direction.

RESULT:

Thus we study and work in Vi Editor

C Programming on UNIX

Ex No: 5: Functions in C

Function:

A function is a complete and independent program, which is used (or invoked) by the mainprogram or other subprograms. A subprogram receives values called arguments from a calling

program, performs calculations and returns the results to the calling program.Advantages of using functions:

There are many advantages in using functions in a program they are:

1. It facilitates top down modular programming. In this programming style, thehigh level logic of the overall problem is solved first while the details of each lower level

functions is addressed later.

2. The length of the source program can be reduced by using functions at appropriateplaces. This factor is critical with microcomputers where memory space is limited.3. It is easy to locate and isolate a faulty function for further investigation.4. A function may be used by many other programs this means that a c programmer can

build on what others have already done, instead of starting over from scratch.

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5. A program can be used to avoid rewriting the same sequence of code at two or morelocations in a program. This is especially useful if the code involved is long or

complicated.6. Programming teams does a large percentage of programming. If the program isdivided into subprograms, each subprogram can be written by one or two team membersof the team rather than having the whole team to work on the complex program

C supports the use of library functions and use defined functions. The library functions are used to

carry out a number of commonly used operations or calculations. The user-defined functions are

written by the programmer to carry out various individual tasks.

Function Definition:

Datatype functionname (argument list);

argument declaration;

{local variable declarations;statements;[return expression];

}Example:

mul(int a,int b){

int y;y=a*b;

return y;}

Types of functions:

A function may belong to any one of the following categories:1. Functions with no arguments and no return values.2. Functions with arguments and no return values.3. Functions with arguments and return values.

1. Functions with no arguments and no return values.

When a function has no arguments it does not receive any data from the calling function.Similarly when it does not return value the calling function does not receive any data from the calledfunction. A function that does not return any value cannot be used in an expression it can be used onlyas independent statement.2. Functions with arguments but no return values:

The nature of data communication between the calling function and the arguments to thecalled function and the called function does not return any values to the calling function.3. Functions with arguments and return values:

The function of the type Arguments with return values will send arguments from the callingfunction to the called function and expects the result to be returned back from the called function backto the calling function.Return value data type of function:

A C function returns a value of type int as the default data type when no other type isspecified explicitly. For example if function does all the calculations by using float values and if thereturn statement such as return (sum); returns only the integer part of the sum. This is since we have

not specified any return type for the sum. There is the necessity in some cases it is important to

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receive float or character or double data type. To enable a calling function to receive a non-integervalue from a called function we can do the two things:

1. The explicit type specifier corresponding to the data type required must be mentioned in thefunction header. The general form of the function definition isType_specifier function_name (argument list)

Argumentdeclaration;

{

functionstatement;

}

The type specifier tells the compiler, the type of data the function is to return.2. The called function must be declared at the start of the body in the calling function, like anyother variable. This is to tell the calling function the type of data the function is actuallyreturning. The program given below illustrates the transfer of a floating-point value betweenfunctions done in a multiple function program.

Void functions:The functions that do not return any values can be explicitly defined as void. This prevents

any accidental use of these functions in expressions.

Ex No: 5a Sorting numbers

Aim: To write a C program to sort n numbers.

Algorithm:

1. Get the number of elements to be sorted.2. Get the array elements to be sorted.3. Sort array of elements by calling the function sort (a, n).4. Print the sorted array of elements.

Program:

#include

void sort(int a[],int n)

{

int i,t,j;

for(i=0;i


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if(a[i]>a[j])

{

t=a[i];

a[i]=a[j];

a[j]=t;

}

}

}

}

printf("The sorted values are :");

for(i=0;i


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Result: Thus the program to sort n numbers was executed and sorted array of elements was

obtained.

Ex.No: 5b Palindrome Checking Using Functions

Aim

To write a C program to find whether the given string is a palindrome or not.

Algorithm

Read a string

Find the length of the string read. Reverse the string.

Compare and check whether the given strings are equal.

Set a flag value

If the flag=1 then the given string is a palindrome.

Otherwise, the given string is not a palindrome.

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Program

#includechar str[50];int len=0,i=0,j,flag=1;main(){

printf("Enter a String:");scanf("%s",str);palindrome();

}

palindrome(){

while(str[i++]!='\0')len++;

for(i=0,j=(len-1);i


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The syntax is as shown below. You start by specifying the type of data stored in the locationidentified by the pointer. The asterisk tells the compiler that you are creating a pointer variable.

Finally you give the name of the variable.Syntax:datatype *variablename;

Example:

int *ptr;

float *string;

Address operator:

Once we declare a pointer variable we must point it to something we can do this by assigningto the pointer the address of the variable you want to point as in the following example:ptr=&num;

This places the address where num is stores into the variable ptr. If num is stored in memory21260 addresses then the variable ptr has the value 21260.Pointer expressions & pointer arithmetic:

Like other variables pointer variables can be used in expressions. For example if p1 and p2are properly declared and initialized pointers, then the following statements are valid.

y=*p1**p2;sum=sum+*p1;

Pointers and function:

The pointers are very much used in a function declaration. Sometimes only with a pointer a

complex function can be easily represented and success. The usage of the pointers in a function

definition may be classified into two groups.

1. Call by reference

2. Call by value

Call by value: When a function is invoked there will be a link established between the formal and

actual parameters. A temporary storage is created where the value of actual parameters is stored. The

formal parameters picks up its value from storage area the mechanism of data transfer between actual

and formal parameters allows the actual parameters mechanism of data transfer is referred as call byvalue. The corresponding formal parameter represents a local variable in the called function. The

current value of corresponding actual parameter becomes the initial value of formal parameter. The

value of formal parameter may be changed in the body of the actual parameter. The value of formal

parameter may be changed in the body of the subprogram by assignment or input statements. This

will not change the value of actual parameters.

Call by Reference: When we pass address to a function the parameters receiving the address should

be pointers. The process of calling a function by using pointers to pass the address of the variable is

known as call by reference. The function, which is called by reference, can change the values of the

variable used in the call.

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Ex No: 6a Swapping two numbers:

Aim: To write a C program to swap two numbers using pointers

Algorithm:

1. Enter the values of a and b2. Swap the numbers by calling the function interchange (&a, &b)3. Print the values of a and b after swapping

Program:

#include

void swap(int *x,int *y)

{

int temp;

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temp=*x;

*x=*y;

*y=temp;

}

main()

{

int a,b;

printf("Enter the value of a and b:");

scanf("%d%d",&a,&b);

swap(&a,&b);

printf("The values of a and b after interchanging:\n");

printf("a=%d\nb=%d",a,b);

printf("\n");

}

Result:Thus the program was executed and the two numbers were swapped using pointers.

Ex No: 6b Sum of n numbers:

Aim: To write a C program to find out sum of n numbers.

Algorithm:

1. Read the value of n2. Get the values3. Perform the summation of given n numbers using pointers

Program:

#include

main()

{

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int a[10];

int n,i,*p,sum=0;

p=a;

printf("Enter the number of values\n");

scanf("%d",&n);

printf(" Enter the values\n");

for(i=0;i


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calloc Allocates space for an array of elements initializes them to zero and returns a

pointer to the memory

free Frees previously allocated space

realloc Modifies the size of previously allocated space.

Allocating a block of memory:

A block mf memory may be allocated using the function malloc. The malloc function reserves

a block of memory of specified size and returns a pointer of type void. This means that we can assign

it to any type of pointer. It takes the following form:

ptr=(cast-type*)malloc(byte-size);

where ptr is a pointer of type cast-type the malloc returns a pointer (of cast type) to an area of memory

with size byte-size.

Example:

x=(int*)malloc(100*sizeof(int));

On successful execution of this statement a memory equivalent to 100 times the area of intbytes is reserved and the address of the first byte of memory allocated is assigned to the pointer x oftype intAllocating multiple blocks of memory:

Calloc is another memory allocation function that is normally used to request multiple blocks

of storage each of the same size and then sets all bytes to zero. The general form of calloc is

ptr=(cast-type*) calloc(n,elem-size);

The above statement allocates contiguous space for n blocks each size of elements size bytes.

All bytes are initialized to zero and a pointer to the first byte of the allocated region is returned. If

there is not enough space a null pointer is returned.

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Releasing the used space:

Compile time storage of a variable is allocated and released by the system in accordance withits storage class. With the dynamic runtime allocation, it is our responsibility to release the spacewhen it is not required. The release of storage space becomes important when the storage is limited.When the data stored in a block of memory is not then the allocated block of memory for future usecan be released , using the free function.

free(ptr);

ptr is a pointer that has been created by using malloc or calloc.

To alter the size of allocate memory:

The memory allocated by using calloc or malloc might be insufficient or excess sometimes in

both the situations we can change the memory size already allocated with the help of the functionrealloc. This process is called reallocation of memory. The general statement of reallocation ofmemory is:

ptr=realloc(ptr,newsize);

This function allocates new memory space of size newsize to the pointer variable ptr and returns a

pointer to the first byte of the memory block. The allocated new block may be or may not be at the

same region.

Ex No: 7a Concatenation of two Strings

Aim: To write C program to concatenate two strings

Algorithm:

1. Get two strings to concatenated2. Concatenate the two strings3. Display the concatenated string

Program:

#include

#include

#define s 40

main()

{

char *s1,*s2,*s3,c;

int i,j,k;

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s1=(char*)malloc(s*sizeof(char));

s2=(char*)malloc(s*sizeof(char));

s3=(char*)malloc(2*s*sizeof(char));

printf("Enter the stirng one:");

scanf("%s",s1);

printf("Enter the stirng two:");

scanf("%s",s2);

i=0;

while((c=*(s1+i))!='\0')

{

*(s3+i)=c;

i=i+1;

}

k=0;

while((c=*(s2+k))!='\0')

{

s3[i+k]=c;

k=k+1;

}

printf("Concatenated string is:\n");

printf("%s\n",s3);

}

Result:

Thus the two was concatenated using the C program.

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ExNo: 7b Altering the allocated memory

Aim: To write a program to alter the allocated memory

Algorithm:

1. Allocate memory space for the character pointer2. Initialize the character pointer with the string MADRAS3. Reallocate memory for storing new string4. Reinitialize the character pointer with new string5. Print the reallocated string

Program:

#include

#include

main()

{

char *p;

p=(char *)malloc(6);

strcpy(p,"MADRAS");

printf("Memory contains:%s\n",p);

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p=(char *)realloc(p,7);

strcpy(p,"CHENNAI");

printf("Memory after altering:%s\n",p);

free(p);

}

Result:

Thus the program to alter the allocated memory was executed and the output was verified.

Ex No: 8 Files in C

Files:

A file is a block of arbitrary information, or resource for storing information, which is

available to a computer program and is usually based on some kind of durable storage. A file is

durable in the sense that it remains available for programs to use after the current program has

finished.

File operations:

C supports a number of functions that have the ability to perform basic file operations, which

include:

1. Naming a file2. Opening a file3. Reading from a file4. Writing data into a file5. Closing a file

Real life situations involve large volume of data and in such cases, the console oriented I/Ooperations pose two major problems

It becomes cumbersome and time consuming to handle large volumes of data throughterminals.

The entire data is lost when either the program is terminated or computer is turned off

therefore it is necessary to have more flexible approach where data can be stored on the disksand read whenever necessary, without destroying the data. This method employs the conceptof files to store data.

File operation functions in C:

Function Name Operation

fopen() Creates a new file for use

Opens a new existing file for use

fclose Closes a file which has been opened for use

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http://en.wikipedia.org/wiki/Computer_programhttp://en.wikipedia.org/wiki/Computer_programhttp://en.wikipedia.org/wiki/Computer_storagehttp://en.wikipedia.org/wiki/Computer_programhttp://en.wikipedia.org/wiki/Computer_storage


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getc() Reads a character from a file

putc() Writes a character to a file

fprintf() Writes a set of data values to a file

fscanf() Reads a set of data values from a file

getw() Reads a integer from a file

putw() Writes an integer to the file

fseek() Sets the position to a desired point in the file

ftell() Gives the current position in the file

rewind() Sets the position to the begining of the file

Defining and opening a file:

In order to store data in a file into the secondary memory, certain things must be specified

about the file to the operating system. They include the fielname, data structure, and purpose. The

general format of the function used for opening a file is

FILE *fp;

fp=fopen(filename,mode);

The first statement declares the variable fp as a pointer to the data type FILE. As stated

earlier, File is a structure that is defined in the I/O Library. The second statement opens the file namedfilename and assigns an identifier to the FILE type pointer fp. This pointer, which contains all the

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information about the file, is subsequently used as a communication link between the system and the

program. The second statement also specifies the purpose of opening the file. The mode does this job.

Ropen the file for read only.W opens the file for writing only.

A open the file for appending data to it.

Consider the following statements:

FILE *p1, *p2;

p1=fopen(data,r);

p2=fopen(results,w);

In these statements the p1 and p2 are created and assigned to open the files data and results

respectively the file data is opened for reading and result is opened for writing. In case the results filealready exists, its contents are deleted and the files are opened as a new file. If data file does not existerror will occur.Closing a file:

The input output library supports the function to close a file; it is in the following format.

fclose(file_pointer);

A file must be closed as soon as all operations on it have been completed. This would close

the file associated with the file pointer.

Observe the following program

.

FILE *p1 *p2;

p1=fopen (Input,w);p2=fopen (Output,r);..

..

fclose(p1);

fclose(p2);

The above program opens two files and closes them after all operations on them arecompleted, once a file is closed its file pointer can be reversed on other file.getc and putc functions:

The getc and putc functions are analogous to getchar and putchar functions and handle one

character at a time. The putc function writes the character contained in character variable c to the file

associated with the pointer fp1. ex putc(c,fp1); similarly getc function is used to read a character from

a file that has been open in read mode. c=getc(fp2).

The getw and putw functions:

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These are integer-oriented functions. They are similar to get c and putc functions and are used

to read and write integer values. These functions would be usefull when we deal with only integer

data. The general forms of getw and putw are:

putw(integer,fp);

getw(fp);

The fprintf & fscanf functions:

The fprintf and scanf functions are identical to printf and scanf functions except that theywork on files. The first argument of theses functions is a file pointer, which specifies the file to beused. The general form of fprintf is

fprintf(fp,control string, list);

Where fp id a file pointer associated with a file that has been opened for writing. The controlstring is file output specifications list may include variable, constant and string.

fprintf(f1,%s%d%f,name,age,7.5);

Here name is an array variable of type char and age is an int variable .The general format of

fscanf is

fscanf(fp,controlstring,list);

This statement would cause the reading of items in the control string.

Example:fscanf(f2,5s%d,item,&quantity);

Like scanf, fscanf also returns the number of items that are successfully read.

Random access to files:

Sometimes it is required to access only a particular part of the and not the complete file. This

can be accomplished by using the fseek function.

fseek function:

The general format of fseek function is a s follows:

fseek(file pointer,offset, position);

This function is used to move the file position to a desired location within the file. Fileptris a pointer to the file concerned. Offset is a number or variable of type long, and position in aninteger number. Offset specifies the number of positions (bytes) to be moved from the locationspecified bt the position. The position can take the 3 values.

Value Meaning

0 Beginning of the file

1 Current file

2 End of the file

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Ex.No: 8a Display the Contents in a File

Aim

To write a C program to display the contents available in a file.

Algorithm

1. Read the file to be displayed.

2. The file to be read is opened in read mode.

3. Read the contents of the file character by character.

4. Print the characters read.

5. Close the file when all its contents are read.

Program#include

main()

{

FILE *fopen(),*fp;

int c;

fp=fopen("Read_File","r");

c=getc(fp);while(c!=EOF)

{

putchar(c);

c=getc(fp);

}

fclose(fp);

}

Result

Thus the C program to read the contents available in a file was written successfully and the

output was verified.

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Ex.No: 8b Reversing a File

Aim

To write a C program to read the contents available in a file and to reverse it.

Algorithm

1. Read the file whose content is to be reversed in read mode.2. Open another file in write mode in to which the reversed information is to be written.

3. Move the file pointer to the end of the file whose contents is to be reversed using the

function fseek().

4. Bring the position back to the last but one character in the file.

5. The function getc() is used to read the next character and after reading, the file

pointer is incremented to the next position.

6. The output thus obtained is displayed in the screen.

Program

#include

main()

{

char ch;

FILE *fp1,*fp2;

fp1=fopen("Input_File","r");

fp2=fopen("Output_File","w");

fseek(fp1,0,2);while(fseek(fp1,-2,1)==0)

{

ch=getc(fp1);

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putchar(ch);

putc(ch,fp2);

}

}

Result

Thus the C program to reverse the contents available in a file was written successfully and the

output was verified.

Ex.No: 8c Transpose Matrix

Aim

To write a C program to find the transpose of a matrix and to write into a file.

Algorithm

1. Initialize a matrix.

2. Open a file write mode into which the transpose matrix is to be written.

3. Perform transpose of a matrix and write the contents into the opened file.

4. The transpose of the matrix is written into the file.

Program

#include

main()

{

int i,j;

int matrix[2][3]={{1,2,3},{4,5,6}};

FILE *fp;

fp=fopen("matrix","w");

fprintf(fp,"\t \n Transpose of the given matrix \n");

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fprintf(fp,"\t%d\t",matrix[j][i]);

fprintf(fp,"\n");

}

}

Result

Thus the C program to write the transpose of a matrix into a file was written successfully and

the output was verified.

computer pratices lab ii (ge 27)

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