C was developed by Dennis Ritchie and evolved from BCPL and B programming languages. C is a hardware-independent language that allows for portable code across different computer systems. A simple C program prints text by using comments, preprocessor directives, and escape characters. Memory in C is represented by variables that have names, types, sizes, and values corresponding to computer memory locations. Data types in C include integers, characters, floating-point numbers, and more.

2. History of C
C language was developed by an American computer programmer Dennis
Ritchie.
C evolved from two previous languages, BCPL and B was developed in
1967 by Martin Richards as a language for writing operating systems
software's and compilers.
C is a hardware independent. With careful design, it is possible to write C
programs that are portable to most computers.

4. A Simple C program : Printing a Line of Text
/*this is my first
program in C */
#include <stdio.h>
int main()
{
printf("Welcome to C n");
return 0;
}
Comments
Preprocessor directive
Method
Escape Character (new line )
Return value

5. A Simple C Program:
Printing a Line of Text
•Comments
• Text surrounded by /* and */ is ignored by computer
• Used to describe program
1 /* NIBM
2 A first program in C */
3 #include <stdio.h>
4
5 void main()
6 {
7 printf( "Welcome to C!n" );
8 }

6. Memory Concepts
•Variables
• Variable names correspond to locations in the
computer's memory.
• Every variable has a name, a type, a size and a value.
• Whenever a new value is placed into a variable (through
scanf, for example), it replaces (and destroys) previous
value
• Reading variables from memory does not change them
• A visual representation
integer1 45

7. Data Types
• C supports several different types of data, each of which
may be represented differently with in the memory.
int Integer quantity
char Single character
float Floating-point number
double Double-precision floating-point number

8. Data Type
printf
conversion
specification
scanf
conversion
specification
int %d %d
short %hd %hd
double %f %lf
float %f %f
char %c %c
unsigned int %u %u

9. Rules For Constructing Variable Name
1. Characters Allowed :
Underscore(_)
Capital Letters ( A – Z )
Small Letters ( a – z )
Digits ( 0 – 9 )
2. Blanks & Commas are not allowed
3. No Special Symbols other than underscore(_) are allowed
4. First Character should be alphabet or Underscore
5.Variable name Should not be Reserved Word

10. Explanation with Example
Tip 1 : Use allowed Characters
Valid Names
num
Num
Num1
_NUM
NUM_temp2

11. Tip 2 : blanks are not allowed
Invalid Names
number 1
num 1
addition of program

12. Tip 3 : No special symbols other that underscore
Valid Identifier
num_1
number_of_values
status_flag

13. Tip 4 : First Character must be underscore or Alphabet
Valid Identifier
_num1
Num
Num_
_
__
Invalid Identifier
1num
1_num
365_days

14. Tip 5 : Reserve words are not allowed
• C is case sensitive.
• Variable name should not be Reserve word.
• However if we capitalize any Letter from Reserve word then it will become
legal variable name.
Valid Identifier
iNt
Char
Continue
CONTINUE
Invalid Identifier
int
char
continue

15. Remember following Tricks
1. Do not Create unnecessarily long variable name
2. Do not use underscore as first character to avoid confusion
between System Variable & user defined variables because many
system variables starts with undescore
3. Variable names are case-Sensitive . i.e sum,Sum,SUM these all
three are different variable names.
4. Reserve words with one/more Capital letters
allowed eg. Int,Float,chAr are allowed but try to skip them.

16. Constants/Literals
A constant is a value or an identifier whose value cannot be
altered in a program.
For example: 1, 2.5, "C programming is easy", etc.
As mentioned, an identifier also can be defined as a constant.
const double PI = 3.14
Here, PI is a constant. Basically what it means is that, PI and
3.14 is same for this program.

17. Below are the different types of constants you can use in C.
1. Integer constants
An integer constant is a numeric constant (associated with number)
without any fractional or exponential part. There are three types of
integer constants in C programming:
decimal constant(base 10)
octal constant(base 8)
hexadecimal constant(base 16)
For example:
Decimal constants: 0, -9, 22 etc
Octal constants: 021, 077, 033 etc
Hexadecimal constants: 0x7f, 0x2a, 0x521 etc
In C programming, octal constant starts with a 0 and hexadecimal
constant starts with a 0x.

18. 2. Floating-point constants
A floating point constant is a numeric constant that has either a
fractional form or an exponent form. For example:
-2.0
0.0000234
-0.22E-5
Note: E-5 = 10-5

19. 3. Character constants
A character constant is a constant which uses single
quotation around characters. For example: 'a', 'l', 'm', 'F'

20. 4. Escape Sequences
Sometimes, it is necessary to use characters which cannot be typed or has special meaning in
C programming. For example: newline(enter), tab, question mark etc. In order to use these
characters, escape sequence is used.
For example: n is used for newline. The backslash ( ) causes "escape" from the normal way
the characters are interpreted by the compiler.
Escape Sequences Character
b Backspace
f Form feed
n Newline
r Return
t Horizontal tab
v Vertical tab
Backslash
' Single quotation mark
" Double quotation mark
? Question mark
0 Null character

21. 5. String constants
String constants are the constants which are enclosed in a pair of
double-quote marks. For example:
"good" //string constant
"" //null string constant
" " //string constant of six white space
"x" //string constant having single character.
"Earth is roundn" //prints string with newline

22. C Integer Input/Output
#include <stdio.h>
int main()
{
int testInteger;
printf("Enter an integer: ");
scanf("%d",&testInteger);
printf("Number = %d",testInteger);
return 0;
}

23. C ASCII Code
#include <stdio.h>
int main()
{
char chr;
printf("Enter a character: ");
scanf("%c",&chr);
// When %c text format is used, character is displayed in case of character types
printf("You entered %c.n",chr);
// When %d text format is used, integer is displayed in case of character types
printf("ASCII value of %c is %d.", chr, chr);
return 0;
}