The document discusses the C programming language. It provides the definition of a program and source code for a simple "Hello World" program in C. It describes how C was developed in 1972 and some key characteristics of C like it being a structured, portable, middle-level language. The document also provides information on variables, data types, constants, and how to compile and run a C program.

2.  Program is a collection of instructions that
will perform some task.
 Source code of a Hello World
program written in the C programming
language
#include <stdio.h>
int main(void)
{
printf("Hello world!n");
return 0;
}

3.  C was developed by Dennis Ritchie at Bell
laboratory in 1972
 It is an upgraded version of languages B and
BCPL.

4.  It is a structured programming language.
 It is highly portable.
 It is a middle level language.
 It is a case sensitive language.
 It uses Top-Down approach.
 It is a Free form language.etc,.

5. GLOBAL DECLARATION SECTION
DOCUMENTATION SECTION
PREPROCESSOR SECTION
DEFINITION SECTION
main()
{
Declaration part;
Executable Part;
}
sub program section
{
Body of the subprogram;
}

6.  Enter the program in a C editor.
 Save the program (File  Save) or F2. Use
the extension .c for saving the file.
Eg: sample.c
 Compile the program(Compile  Compile)
or Alt+F9.
 Run the program(Run  Run) or Ctrl+F9.

7.  Enter the program in vi editor.
 Save the file using :wq
Use the extension .c for saving the file.
Eg: sample.c
 Compile the program.
Eg: cc sample.c (or) gcc sample.c
 Run the program using a.out.

8.  Identifiers are names given to various
program elements such as functions and
arrays etc,.
› Example:
int total,marks;
› Here total and marks are user defined
identifiers.

9.  First character must be alphabetic or underscore.
 Must consist only of alphabetic characters, digits, or
underscores.
 Only the first 31 characters of an identifier are
significant and are recognized by the compiler.
 Cannot use a keywords or reserved word (e.g. main,
include, printf & scanf etc.).
 No space are allowed between the identifiers etc,.
 C is case sensitive, e.g. My_name  my_name.

10. Valid Names Invalid Names
a a1 $sum /* $ is illegal */
student_name stdntNm 2names /* Starts with 2 */
_aSystemName _anthrSysNm stdnt Nmbr /* no spaces */
TRUE FALSE int /* reserved word */
Variables :
Variable is an identifier that is used to represent some
specified type of information.
Eg: x=3 Here x is variable.

11. auto register continue
double typedef for
int char signed
struct extern void
break return default
else union goto
long const sizeof
switch float do
case short if
enum unsigned
static while
It is a reserved word, which cannot be used for
anything else. Examples:

12. Constants
Character Constants
Numeric Constants
Real
Constant
Integer
Constant
String
Constant
Single
Character
Constant
Constants
Numeric Constants
Integer
Constant
Constants
Numeric Constants
Real
Constant
Integer
Constant
Constants
Numeric Constants
Single
Character
Constant
Real
Constant
Integer
Constant
Constants
Numeric Constants
String
Constant
Single
Character
Constant
Real
Constant
Integer
Constant
Constants
Numeric Constants
Constants
Numeric Constants Character Constants
Numeric Constants
It is an entity whose value does not changes during
the execution.

13. Integer constants
 It is formed using a sequence of digits.
Decimal - 0 to 9 .
Octal - 0 to 7.
Hexa - 0 to 9 ,A to F
Eg: 10,75 etc.
Rules for defining Integer Constant:
 It must have at least one digit.
 Decimal point are not allowed.
 No blank space or commas are allowed.
 It can be either positive or negative. Etc,.

14. Real constants
 It is formed using a sequence of digits but it
contain decimal point.
 length, height, price distance measured in
real number.
Eg: 2.5, 5.11, etc.

15. Single character constant
A character constant is a single character they
also represented with single digit or a single
special symbol which is enclosed in single quotes.
Eg: ‘a’, ‘8’,’_’etc.
String constants
 String constant are sequence of characters
enclosed with in double quote.
Eg: “Hello” ,”444”,”a” etc,.

16. Data Types
A data type is a classification identifying one of various
types of data, such as real-valued, integer or Boolean,
that determines the possible values for that type

17.  A number without a fraction part : integral number.
 Integer occupies 2 Bytes.
 The Control or Format String for integer is %d.
 C supports three different sizes of the integer
data type :
 short int
 int
 long int

18.  A floating-point type is a number with a
fractional part, e.g. 56.78.
 Floating point numbers occupies 4 Bytes.
 The Control or Format String for float is %f.
 C supports three different sizes of the float data
type
 Double
 float
 long double

19.  Character are generally stored using 8 bits(1 Byte)
of the internal storage.
 The Control or Format String for Character is %c.
Character ASCII code value
a 97(decimal) or 01100001(binary)
x 120(decimal) or 01111000(binary)

20.  The void type has no values and no operations.
 Both the set of values and the set of operations
are empty.

21. Data type Size(bytes) Range Format string
(or)Control String
Char 1 128 to 127 %c
Unsigned char 1 0 to 255 %c
Short or int 2 -32,768 to 32,767 %i or %d
Unsigned int 2 0 to 65535 %u
Long 4 -2147483648 to 2147483647 %ld
Unsigned long 4 0 to 4294967295 %lu
Float 4 3.4 e-38 to 3.4 e+38 %f or %g
Double 8 1.7 e-308 to 1.7 e+308 %lf
Long Double 10 3.4 e-4932 to 1.1 e+4932 %lf

22.  To create a variable, you must specify
the type.
Example: float price;
int a,b;
char code;