1. C programs consist of functions that perform specific tasks. The main() function is where program execution begins. 2. This example program prints "Welcome to C" by using functions like printf() to output text and getch() to pause the program. 3. The #include directives tell the compiler to include header files containing declarations for functions like printf() and clrscr() that are used in the program.

1. Basic Programs in C

2. Structure Of C Program
• C programs consist of one or more functions. Each function
performs a specific task. A function is a group or sequence of
C statements that are executed together.
• The following is a simple C program that prints a message on
the screen.
/* A simple program for printing a message */
# include <stdio.h>
# include <conio.h>
void main( )
{
clrscr( );
printf(“Welcome to C”);
getch( );
}

3. Description
• The first line
/* A simple program for printing a message */
is a comment line. Comments in the c program are optional
and may appear anywhere in a C program. Comments are
enclosed between /* and */.
• The second line
# include <stdio.h>
tells the compiler to read the file stdio.h and include its
contents in this file. stdio.h, one of header files, contain the
information about input and output functions. stdio.h means
Standard Input Output Header file. This file contains the
information about printf() function.

4. Description (contd..)
The third line
# include <conio.h>
• tells the compiler to read the file conio.h and include its contents in this
file. conio.h means Consoled Input Output Header file. This file contains
the information about clrscr() and getch() functions.
The fourth line
void main( )
• is the stat of the main program. The word main is followed by a pair of
ordinary parenthesis ( ), which indicates that main is also a function.
The fifth line
{
• the left brace represents the beginning of the program.
The sixth line
clrscr( );
• tells the compiler to clear the screen and kept the cursor at left side
corner.

5. Description (contd..)
The seventh line
printf( “Welcome to C”);
this function causes its arguments to be printed on the
screen on the computer.
The eight line
getch( );
is reads the single character directly from the keyboard
without printing on the screen.
The ninth line
}
the right brace represents the ending of the program.

6. Writing a C program
1. All C statements must end with semicolon.
2. C is case-sensitive. That is, upper case and lower case
characters are different. Generally the statements are typed
in lower case.
3. A C statement can be written in one line or it can split into
multiple lines.
4. Braces must always match upon pairs, i.e., every opening
brace { must have a matching closing brace }.
5. Every C program starts with void main( ) function.
6. Comments cannot be nested. For example,
/* Welcome to ‘C’ ,/* programming*/ */
– A comment can be split into more than one line.

7. Execution of C Program
Steps to be followed in writing and running a C program.
• Creation of Source Program
Create a C program file in various C compilers are available
under MS-DOS, Turbo C Editor etc.
• Compilation of the Program
Turbo C compiler is user friendly and provides integrated
program development environment. Thus, selecting key
combination can do compilation. That means press Alt +
F9 for compilation.
• Program Execution
In Turbo C environment, the RUN option will do the
compilation and execution of a program. Press Ctrl + F9
for execution the program.

8. Execution

9. Printf() Function
• The printf( ) function is used to write information to standard
output (normally monitor screen). The structure of this function is
• printf(format string, list of arguments); e.g. printf(“%d”,a)
The format string contains the following:
• Characters that are simply printed on the screen.
• Specifications that begin with a % sign and define the output
format for display of each item.
• Escape sequence characters that begin with a sign such as n, t
etc Character Argument Resulting Output
c Character A single character
d Integer Signed decimal integer
s String Prints character strings
f Floating Single floating point number
point

10. Scanf(),Getting input from user
• The real power of a technical C program is its ability to
interact with the program user. This means that the
program gets input values for variables from users.
• The scanf( ) function is a built-in C function that
allows a program to get user input from the keyboard.
The structure of this function is
• scanf(format string &list of arguments);
Examples
• scanf(“%d”, &a );
• scanf(“%d %c %f ”,&a, &b, &c );

11. Control Structures
• The control flow statements of a language determine
the order in which the statements are executed.
• We also need to be able to specify that a statement, or a
group of statements, is to be carried out conditionally,
only if some condition is true.
• Also we need to be able to carry out a statement or a
group of statements repeatedly based on certain
conditions.
• These kinds of situations are described in C using
Conditional Control and Loop Control structures.

12. Conditional & Loop Structure
A conditional structure can be implemented in C
using
• The if statement
• The if-else statement
• The nested if-else statement
• The switch statement.
Whereas loop control structures can be implemented
in C using
• while loop
• do-while loop
• for statement

13. The ‘If’ Statement
• The if statement is used to control the flow of execution of
statements. The general form of if statement is
• if (condition)
• statement;
Suppose if it is required to include more than one statement, then
a compound statement is used, in place of single statement.
The form of compound statement is
• if (condition)
• {statement1;
statement2;
}
• If the condition is true, then the statements will be executed.
If the condition is false, then the statement/statements will not
be executed.

14. If –else statement
The general form of if-else statement is…
• if (condition)
statement1;
else
statement2;
• If the condition is true, then statement1 is executed. Otherwise if the
condition is false, then the statement2 is executed. Here statements
statement1 and statement2 are either simple statements or compound
statements.
• if (condtion)
{ statements /* if block */
}
else
{ statements /* else */
}

15. Example of ‘If-else’
/* Inputting year is Leap or not */
#include<conio.h>
#include<stdio.h>
int main(){
Sample output:
Enter any year: 2010
int year; 2010 is not a leap year
printf("Enter any year: ");
scanf("%d",&year); Enter any year: 2100
if((year%4)==0) 2100 is not a leap
year
printf("%d is a leap year",year);
else Enter any year: 2000
printf("%d is not a leap year", year); 2000 is a leap year
return 0;
}

16. Example
• // Single digit or not
#include<stdio.h>
#include<conio.h> Output 1
void main() Enter a number:5
{ int n; Single digit
clrscr(); Output 2
Enter a number:12
printf(“Enter a number:”);
Not single digit
scanf(“%d”,&n);
if(n<=9)
printf(“Single digit”);
else
printf(“Not single digit”);
getch(); }

17. Nested If-else
/* A quick demo of nested if-else */
• We can also write an main( )
entire if-else {
construct within int i ;
printf ( "Enter either 1 or 2 " ) ;
either the body of the scanf ( "%d", &i ) ;
if statement or the if ( i == 1 )
body of an else printf ( "You have entered 1" ) ;
statement. else
{
• This is called ‘nesting’ if ( i == 2 )
of ifs. This is shown printf ( " You have entered 2" );
in the program. else
printf ( “You have entered wrong entry”) ;
}
}

18. Decision Using Switch
• The control statement that allows us to make a decision from
the number of choices is called a switch, or more correctly a
switch case-default, since these three keywords go together
to make up the control statement. They most often appear as
follows:
switch ( integer expression )
{ case constant 1 :
do this ;
case constant 2 :
do this ;
case constant 3 :
do this ;
default :
do this ;}

19. Without Break keyword
• The integer expression following main( )
the keyword switch is any C {
int i = 2 ;
expression that will yield an
switch ( i )
integer value. {
• It could be an integer constant case 1 :
like 1,2 or an expression that printf ( "I am in case 1 n" ) ;
evaluates to an integer. case 2 :
• The keyword case is followed by printf ( "I am in case 2 n" ) ;
case 3 :
an integer or a character
printf ( "I am in case 3 n" ) ;
constant. Each constant in each default :
case must be different from all printf ( "I am in default n" );
the others. }
}

20. Use of Break
• If you want that only case main( )
2 should get executed, it {
is up to you to get out of int i = 2 ;
the switch then and there switch ( i )
{
by using a break
case 1 :
statement.
printf ( "I am in case 1 n" ) ;
Note :-there is no need for a break ;
break statement after the case 2 :
default, since the control printf ( "I am in case 2 n" ) ;
comes out of the switch break ;
anyway. case 3 :
printf ( "I am in case 3 n" ) ;
break ;
default :
printf ( "I am in default n" ) ;
}

21. Flowchart

22. Examples
main( )
{
int i = 22 ;
switch ( i )
{
case 121 :
printf ( "I am in case 121 n" ) ; • The output of
break ; this program
case 7 : would be:
printf ( "I am in case 7 n" ) ;
break ; I am in case 22
case 22 :
printf ( "I am in case 22 n" ) ;
break ;
default :
printf ( "I am in default n" ) ;
}
}

23. Examples
main()
{ •The output of this
char c = 'x' ;
program would be:
switch ( c )
{
I am in case x
case 'v' :
•In fact here when we
printf ( "I am in case v n" ) ;
break ;
use ‘v’, ‘a’, ‘x’ they are
case 'a' : actually replaced by the
printf ( "I am in case a n" ) ; ASCII values (118, 97,
break ; 120) of these character
case 'x' : constants.
printf ( "I am in case x n" ) ;
break ;
default :
printf ( "I am in default n" ) ;}}

24. Some Points about Switch-Case
• A float expression cannot be tested using a switch
• Cases can never have variable expressions (for example it is
wrong to say case a +3 : )
• Multiple cases cannot use same expressions. Thus the
following switch is illegal
• switch ( a )
{
case 3 :
...
case 1 + 2 :
….
}

25. goto Keyword
• The use of goto should be avoided because after using it
programs become unreliable, unreadable and hard to debug.
• In a difficult programming situation it seems so easy to use a
goto to take the control where you want.
• The big problem with gotos is that when we do use them we
can never be sure how we got to a certain point in our code.
• They obscure the flow of control. So as far as possible skip
them.

26. Example
main()
{ int goals ;
printf ( "Enter the number of goals scored against England" ) ;
scanf ( "%d", &goals ) ;
if ( goals <= 5 )
goto sos ;
else
{
printf ( “soccer players n“ );
printf ( “Say goodbye to soccer" ) ;
exit( ) ; /* terminates program execution */
}
sos :
printf ( “Out of the execution!" ) ;}

27. • If the condition is satisfied the goto statement transfers
control to the label ‘sos’, causing printf( ) following sos to
be executed.
• The label can be on a separate line or on the same line as the
statement following it, as in,
sos : printf ( "To err is human!" ) ;
Any number of gotos can take the control to the same label.
The exit( ) function is a standard library function which
terminates the execution of the program. It is necessary to
use this function since we don't want the statement
printf ( “Out of Execution”);
to get executed after execution of the else block.