The document contains 18 questions asking to write C programs for various tasks. These include swapping two numbers, finding roots of a quadratic equation, converting between Celsius and Fahrenheit scales, calculating simple interest, finding the sum and maximum of numbers, checking even/odd and positive/negative status, performing arithmetic operations using switch case, reversing numbers, and more. The document provides algorithms and sample C code to solve each problem.

1. INDEX
1. Explain dos internal and external commands?
2. Write a C program for swapping of two numbers?
3. Write a C program to Find the roots of quadratic equation?
4. Write a C program to find centigrade value
C=(f-32)5/9
5. Write a C program to Find simple interest
I=p*t*r/100
6. Write a C program to find sum of ‘n’ numbers?
7. Write a C program to find the biggest of two numbers?
8. Write a C program to check that given number is even or odd?
9. Write a C program to check the given no is +ve or –ve?
10.Write a C program to find the biggest of 3 elements?
11.Write a C program to perform Arithmetic operation using switch case?
12.Write a C program to calculate Reverse of given numbers?
13.Write a C program to find Sum of digits of a given numbers?
14.Write a C program to Print 1-10 even numbers?
15.Write a C program to Check prime number or not?
16.Write a C program to find Factorial of a given number?
17.Write a C program to find Sum of element of array?
18.Write a C program to find the length of the string?
19.Write a C program to print a multiplication table?

2. 1) Explain dos internal and external commands?
*MS-DOS (Microsoft-Disk Operating System):
Gary kildall of Digital Research developer developed the first popular
operating system for microcomputers (PC) in 1974. It was named CPM (Control
Program for Microcomputers) and it created incompatibility (the software
developed for one computer would not run on another computer).
IBM and Microsoft Company developed an operating system named as
PC-DOS (Personal Computer-Disk Operating System). After that PC-DOS name
was changed as MS-DOS.
*HOW TO OPEN COMMAND PROMPT:
Click on START menu on the system toolbar, a pop-up menus are visible, in that
select RUN menu, a dialog box will appear. In that we type COMMAND or CMD
and click on ENTER key. It will display the command prompt.
Program:
Program is a set of various instructions that are using a computer language.
*FILE:
File is a collection of text or data that are logically related. A file is identified
with its name. Naming of a file normally has two parts-File Name and File
Extension.
File name can be at most eight characters long. Characters can be either
lowercase letters or uppercase letters or numbers or some special characters also.
Some of the file extensions are .exe, .bat, .doc, .txt, etc.
Text files:
These are the files used to stored data. These are the files used to store inputs as
well as output data of the program.
Batch files:
These contain a set of instructions that are to be executed as a batch in a
sequential order. These files are usually used to perform a specific task.

3. Application program files:
These are usually application specific used to perform specific task. Word
processors, spreadsheets are some of the application program files.
*DIRECTORY:
A directory is a logical grouping of files. A directory contains the name of the
files, along with their extensions, the file size, and the date of creation.
*STRUCTURE OF MS-DOS DISK:
MS-DOS divides the disk into two parts are system area and Data area
1. System Area:
This area is used to keep track of any vital information about disk. This
system area uses very small portion (2 %) of the total disk.
This system area is further divided into BOOT Area, FAT Area and ROOT
Directory.
Boot area:
It is also known as BOOT RECORD. This area stores the program, which
is used to do the task of beginning and loading the MS-DOS into the memory of
the computer. This process is called booting process.
Fat (File Allocation Table) area:
This area is used to manage the big data portions of the disk and to record
the status of each area of the disk.
Root Directory:
This is the file directory used to record the files that are stored on the disk.
2. Data area:
It is the bigger part of the disk, where the data files are stored on the disk.
* Naming a file in MS-DOS:
Every file stored on the disk is given a filename, which should be unique.
The file can be of 8.3 characters i.e. name maximum of eight characters, + ’.’ +

4. maximum of three characters extension. If number of characters specified is more
than 8.3, DOS will take only 8.3 characters and truncate the rest.
* Characteristics of MS-DOS:
• Every DOS commands have to be typed at the DOS prompt in either upper or
lower case.
• Each command is executed by pressing ENTER key.
• Maximum length of a DOS command cannot exceed 127 characters.
• Pressing CTRL+C or CTRL+Z to cancel the command under execution.
*File Specification:
Along with the filename, a drive specifies may be given while referring to a file.
E.g.: C: SAMPLE. TXT
Drive File Name Extension
* Changing the drives:
If we are in C drive. C:>
If we want to change the drive D, just write drive name followed by :(Colon
symbol).
E.g.: C:> D:
* COMMANDS IN MS-DOS:
• Internal commands
• External commands
Internal commands:
Internal commands are in-built commands of MS-DOS.
MD: This command is used to create a new directory.
Syntax: md directory-name. E.g.: c:> md gvp

5. CD: This command is used to change from one directory to another directory.
Syntax: cd directory-name. E.g.: c:> cd gvp
RD: This command is used to remove a current directory.
Syntax: rd directory-name. E.g.: c:> rd gvp
DATE: This command displays the current system date and we can set or modify the
system date.
Syntax: date E.g.: C:> date
TIME: This command displays the current system time and we can set or modify the
system time.
Syntax: time E.g.: C:> time
DIR: This command displays the list of file names and directory names of the current drive.
Syntax: dir E.g.: C:> dir
Options:
CLS:
This command is used to clear the text on the display screen.
Syntax: cls E.g.: C:>cls
TYPE: This command displays contents of specified file.
Syntax: type file-name E.g.: C:> type gvp.txt
COPY: This command is used to copies one or more files to specified file.
Syntax: copy old-name new-name E.g.: C:> copy gvp.txt gvpdegree.txt
COPY CON: To create a file and insert the information into that file we used copy con
command.
Syntax: copy con file-name E.g.: copy con gvp.txt

6. This command inserts the data on current file. If we want to stop the inserting information
press CTRL+Z.
RENAME / REN: This command is used to Change the name of specified file or directory.
Syntax: ren old-name new-name E.g.: C:> ren gvp.txt gvpdegree.txt
DEL: This command is used to delete the specified file.
Syntax: del file-name E.g.: C:> del gvp.txt
TREE: This command displays the sub-directories and files as tree structure of current
directory.
Syntax: <path> tree E.g.: C:> gvpgvpdegree tree
VER: This command displays the DOS version number that is being used.
VOL: This command displays the disk volume label of the specified drive.
External commands:
The external commands are separate programs that reside on external devices (floppy, cd or
hard disk). Loading it from external devices to main memory of the computer can use these
commands.
PRINT: It is used to print the current document.
Syntax: print file-name E.g.: C:> print gvpdegree.txt
FORMAT: It is used to format the current drive in the computer system.
Syntax: format: drive-name E.g.: C:> format: C
LABEL: It is used to change the label of current drive.
SYS: It is used to transfer the operating system files from one drive to another drive.
DISKCOPY: It is used to copy the disk and transfer the information into another disk.
CHKDSK: It is used to scan the disk in the specified drive and checks it for

7. 2) Write a C program for swapping of two numbers?
Algorithm:
Program:
#include <stdio.h>
main()
{
int x, y, temp;
printf("Enter the value of x and yn");
scanf("%d%d", &x, &y);
printf("Before Swappingnx = %dny = %dn",x,y);
temp = x;
x = y;
y = temp;
printf("After Swappingnx = %dny = %dn",x,y);
}
Output:
Enter the value of x and y
x= 10
y=20
Before swapping
x=10
y=20
After swapping
x=20
y=10

8. 3) Write a C program to Find the roots of quadratic equation?
Algorithm:
Program:
#include<stdio.h>
#include<conio.h>
#include<math.h>
void main()
{
int a,b,c,d,e,f,g;
clrscr();
printf(“Enter the three values”);
scanf(“%d%d%d”,&a,&b,&c);
d=((b*b)-(4*a*c));
if(d==0)
{
printf(“Roots are real and equal”);
f=-b/(2*a);
printf(“x1=%dnx2=%d”,f,f);
}
else if(d>0)
{
printf(“Roots are real and distinct”);
e=sqrt(d);
f=(-b+e)/(2*a);
g=(-b-e)/(2*a);
printf(“x1=%dnx2=%d”,f,g);
}
else
{
printf(“Roots are imaginary”);
d=-d;
e=sqrt(d);
f=-b/(2*a);
g=e/(2*a);
printf(“x1=%d+%dnx2%d-%d”,f,g,f,g);
}
getch();
}
Output:
Enter the three values:
a=2 b=5 c=3
d=25-24=1
Roots are real and distinct:
x1= -1
y1= -1.5

9. 4) Write a C program to find centigrade value
C=(f-32)5/9
Algorithm:
Program:
#include <stdio.h>
main ()
{
int fahrenheit;
double celsius;
printf("Enter the temperature in degrees Fahrenheit:nnnn");
scanf("%d", &fahrenheit);
celsius = (5/9) * (fahrenheit-32);
printf ("The converted temperature is %lfn", celsius);
}
Output:
Enter the temperature in degrees Fahrenheit: 5
The converted temperature is= -15

10. 5) Write a C program to Find simple interest
I=p*t*r/100
Algorithm:
Program:
#include<stdio.h>
#include<conio.h>
main()
{
float p,rate,time,si;
printf("Enter principal amount : ");
scanf("%f", &p);
printf("Enter rate of interest : ");
scanf("%f", &rate);
printf("Enter time period in year : ");
scanf("%f", &time);
/*calculating simple interest*/
si=(p*time*rate)/100;
printf("nSimple Interest = %2f",si);
getch();
}
Enter principal amount : 1000
Enter rate of interest : 2.5
Enter time period in year : 2
Simple Interest = 50

11. 6) Write a C program to find sum of ‘n’ numbers?
Algorithm:
Program:
#include<stdio.h>
#include<conio.h>
main()
{
int s=0,i=1,n;
clrscr();
printf("Enter a value ");
scanf("%d",&n);
while(i <= n)
{
s=s+i;
i=i+1;
}
printf("Sum of first %d natural numbers is %d",n,s)
getch();
}
Output:
Enter a value = 5
Sum of first 5 natural numbers is = 15

12. 7) Write a C program to find the biggest of two numbers?
Algorithm:
Program:
#include <stdio.h>
main()
{
int i,j,big;
printf(“Enter any two numbers”);
scanf("%d%d",&i,&j);
if(i < j)
{
big = j;
}
else
{
big = i;
}
printf("biggest of two numbers(using else) is %d n",big);
}
Output:
Enter any two numbers:
i=15
j=29
biggest of two numbers(using else) is = 29

13. 8) Write a C program to check that given number is even or odd?
Algorithm:
Program:
#include<stdio.h>
main()
{
int n;
printf("Enter an integern");
scanf("%d",&n);
if ( n%2 == 0 )
printf("Evenn");
else
printf("Oddn");
}
Output:
Enter an integer:5
Odd

14. 9) Write a C program to check the given no is +ve or –ve?
Algorithm:
Program:
#include<stdio.h>
#include<conio.h>
void main()
{
int n;
clrscr();
printf("enter the no");
scanf("%d",&n);
if(n>=0)
printf("nnumber is +ve");
if(n<0)
printf("n number is -ve");
getch();
}
Output:
enter the no : 36
nnumber is +ve

15. 10) Write a C program to find the biggest of 3 elements?
Algorithm:
Program:
#include<stdio.h>
#include<conio.h>
main()
{
int a,b,c;
printf(“Enter any three numbers n”);
scanf(“%d%d%d”,&a,&b,&c);
if(a > b)
{
if(a > c)
{
big = a;
}
else
{
big = c;
}
}
else
{
if(b > c)
{
big = b;
}
else
{
big = c;
}
}
printf(“Biggest number of given three numbers = %d “,big);
getch();
}
Output:
Enter any three numbers:
a=23
b=34
c=22
Biggest number of given three numbers = 34

16. 11)Write a C program to perform Arithmetic operation using switch case?
Algorithm:
Program: #include<stdio.h>
#include<conio.h>
void main()
{
int n1, n2, ch ;
clrscr() ;
printf("Enter the first number : ") ;
scanf("%d", &n1) ;
printf("nEnter the second number : ") ;
scanf("%d", &n2) ;
printf("1 -> Addition n ") ;
printf("2 -> Subtraction n ") ;
printf("3-> Multiplication n ") ;
printf("4 -> Division n ") ;
printf("nnEnter your choice <1...4> : ") ;
scanf("%d", &ch) ;
switch(ch)
{
case 1 :
printf("n%d + %d = %d", n1, n2, n1 + n2) ;
break ;
case 2 :
printf("n%d - %d = %d", n1, n2, n1 - n2) ;
break ;
case 3 :
printf("n%d * %d = %d", n1, n2, n1 * n2);
break ;
case 4 :
printf("n%d / %d = %.2f", n1, n2, (float)n1 / n2);
break ;
default :
printf("nInvalid choice");
break ;
}
getch();
}
Output: Enter the first number : 5 Enter the second number : 6
1 -> Addition 2 -> Subtraction 3-> Multiplication 4 -> Division
Enter your choice <1...4> : 1
11

17. 12) Write a C program to calculate Reverse of given numbers?
Algorithm:
Program:
#include <stdio.h>
main()
{
int n, reverse = 0;
printf("Enter a number to reversen");
scanf("%d",&n);
while (n != 0)
{
reverse = reverse * 10;
reverse = reverse + n%10;
n = n/10;
}
printf("Reverse of entered number is = %dn", reverse);
}
Output: Enter a number to reverse : 235
Reverse of entered number is = 532

18. 13) Write a C program to find Sum of digits of a given numbers?
Algorithm:
// sum of the digits of num
Step 0 : start
Step 1 : declare main function
Step 2 : int n, sum = 0, remainder;
Step 3: input n value
Step 4: loop until we have no digits left to process
while(n != 0)
{
step 4.1: find out the rightmost digit
remainder = n % 10;
step 4.2: add the rightmost digit to our sum
sum = sum + remainder;
step 4.3: remove the rightmost digit from num
n = n / 10;
}
Step 5: print sum value
Step 6 : stop
}
Program:
#include <stdio.h>
main()
{
int n, sum = 0, remainder;
printf("Enter an integern");
scanf("%d",&n);
while(n != 0)
{
remainder = n % 10;
sum = sum + remainder;
n = n / 10;
}
printf("Sum of digits of entered number = %dn",sum);
}
Output:
Enter an integer : 123
Sum of digits of entered number = 6

19. 14) Write a C program to Print 1-n even numbers?
Algorithm:
Program:
main()
{
int i,num;
printf(“Enter any number”);
scanf(“%d”,&num);
for(i=0;i<=num;i++)
if(num%2==0)
printf(“%d”,num);
}
Output:
Enter any number: 10
1
2
3
4
5
6
7
8
9
10

20. 15) Write a C program to display prime numbers ?
Algorithm:
Program:
#include<stdio.h>
main()
{
int n, i = 3, count, c;
printf("Enter the number of prime numbers requiredn");
scanf("%d",&n);
if ( n >= 1 )
{
printf("First %d prime numbers are :n",n);
printf("2n");
}
for ( count = 2 ; count <= n ; )
{
for ( c = 2 ; c <= i - 1 ; c++ )
{
if ( i%c == 0 )
break;
}
if ( c == i )
{
printf("%dn",i);
count++;
}
i++;
}
}
Output:
Enter the number of prime numbers required:10
First 10 prime numbers are :
2
3
5
7

21. 16) Write a C program to find Factorial of a given number?
Algorithm:
Program:
#include<stdio.h>
int main()
{
int i=1,f=1,num;
printf("Enter a number: ");
scanf("%d",&num);
while(i<=num)
{
f=f*i;
i++;
}
printf("Factorial of %d is: %d",num,f);
return 0;
}
Sample output:
Enter a number: 5
Factorial of 5 is: 120

22. 17) Write a C program to find Sum of element of array?
Algorithm:
Program:
#include <stdio.h>
#include<conio.h>
main()
{
int a[10] = {1, 2, 0, 0, 4, 5, 6, 9, 9, 17};
int sum=0;
clrscr();
printf("nArray:n");
for(int i=0;i<10;i++)
sum = sum + a[i];
printf("The sum is %dn", sum);
getch();
}
Output:
The sum is = 53

23. 18) Write a C program to find the length of the string?
Algorithm:
Program:
#include <stdio.h>
void main()
{
char string[50];
int i, length = 0;
printf("Enter a stringn");
gets(string);
for (i=0; string[i] != '0'; i++)
{
length++;
}
printf("The length of a string is the number of characters in itn");
printf("So, the length of %s =%dn", string, length);
}
/*----------------------------------------------------
Output
Enter a string
hello
The length of a string is the number of characters in it
So, the length of hello = 5

24. 19) Write a C program to print a multiplication table?
Algorithm:
Program:
#include <stdio.h>
int main()
{
int num, i = 1;
printf(" Enter any Number:");
scanf("%d", &num);
printf("Multiplication table of %d: ", num);
while (i <= 10)
{
printf(" %d x %d = %d", num, i, num * i);
i++;
}
return 0;
}
Output:
Enter any Number:5
5x1=5
5 x 2 = 10
5 x 3 = 15
5 x 4 = 20
5 x 5 = 25
5 x 6 = 30
5 x 7 = 35
5 x 8 = 40
5 x 9 = 45
5 x 10 = 50

25. 20) Write a program to display 'n' natural numbers using for loop..(in C).....
Algorithm:
Program:
#include<stdio.h>
main()
{
int n,i;
printf("n Enter the range......Please...t");
scanf("%d",&n);
printf("n Range of Natural Numbers.....t");
for(i=1;i<=n;i++)
{
printf("t%d",i);
}
}
Output:
Enter the range......Please... = 10
Range of Natural Numbers.....
1
2
3
4
5
6
7
8
9
10