C-programming theory

C-Programming Language

Introduction

         It is a structured programming language, uses simple English word with some mathematical expression, has a high speed and easy to understand. It is also termed as middle level language or intermediate language between high level and low level language. It is very powerful programming language because it is used to prepare system software as well as application software. It has large numbers of vocabularies and syntax to write program. It was developed by Dennis Ritchie in 1970, USA.

Why to use C?

a.   C is a powerful and flexible language so system software and application software can be developed.

 b.   C is a popular language preferred by professional as it has wide variety of c-compilers and accessories.

 c.   C is a portable language so can be compiled and run on another system too.

d.   Those words which has special meaning to a language compiler (called keyword or reversed word), can be used to do any task while making program.

e.   C is a modular so subroutines can be reused in other applications or programs.

Features of C-Language

         It is a popular language because it has large number of features for programmer to write medium types of program. Some features of it are given below:

a.   It is highly portable language.

b.   It is procedural programming language because program is divided into number of functions.

c.   It inherits or invisible functionality(memory management, CPU register manipulation, etc.)

d.   It is general purpose structured programming language.

e.   It is internationally standardized programming language.

Advantages

a.   It is very easy for debugging, testing and maintaining.

b.   It is portable so can be run in any computer.

c.   It is fast for executing.

d.   The statement in C-language are generally short but very powerful.

e.   It has only 32 keywords so that easy to remember.

Disadvantages

         C-language has not strong disadvantages but has some negligible disadvantages which are given below:

a.   There is no runtime checking.

b.   As the program extends it is very difficult to fix the bug.

c.   It may be compile time overhead due to the misplacing and excessive use of pointers.

d.   It does not use to develop complex type of software nowadays.

e.   Object oriented programming concept is not included in C.

Fundamental of C

         C - Character sets are letters, digits, and special characters and white spaces that form words, numbers and expressions allowed to use in C programming language.

The following character sets are used in C.

         Letters                           Digits

Upper case A to Z                   0 to 9

Lower case a to z

Special characters

,	Coma	.	Period
;	Semicolon	:	Colon
?	Question mark	'	Apostrophe
"	Quotation marks	!	Exclamation mark
|	Vertical bar	/	Slash
\	Back slash	~	Tilde
_	Underscore	$	Dollar sign
%	Percentage sign	&	Ampersand
^	Caret	*	Asterisk
-	Minus sign	+	Plus sign
<	Opening angle	>	Closing angle
(	Left parenthesis	)	Right parenthesis
[	Left bracket	]	Right bracket
{	Left brace	}	Right brace
#	Hash

White space

white space is any section of a document that is unused or space around an object

- Blank line  - Horizontal Tab   - Carriage Return   - New line   - Form feed

Comments:

         Comments in code can be useful for various purpose such as for providing visual split between various parts of the code, gives information about the code that what is going to do, etc.

Comments can be written in two Forms:

//single line comments

/*multi-line comments*/

Tokens:

Tokens are fundamental parts of C program from which other parts are formed. There are six types of C tokens that are listed below:

a) Operators b) Keywords c) Identifiers d) Constants e) strings f) Special symbols

Keywords or reserved words

C keeps a small set of keywords for its own use. These keywords cannot be used as identifiers in the program. It has special meaning in the program to a language compiler that are pre defined in C programming language.

Auto	Double	Int	Struct
Break	Else	Long	Switch
Case	Enum	Register	Typedef
Char	Extern	Return	Union
Const	Float	Short	Unsigned
Continue	For	Signed	Void
Default	Goto	Sizeof	Volatile
Do	If	Static	While

Identifiers

         Identifiers are the names given to program unit such as variable, structure, etc. They are not defined in programming language but are used to define by the programmer. Some basic rules to define identifiers are given below:

a.   First character must be an alphabet underscore then digits or alphabets.

b.   It must consist of only letters, digits and underscore.

c.   Any standard C language keyword cannot be used as identifier name.

d.   It should not be contain a space.

e.   It allows both upper case and lower case characters.

Valid Identifier: B1, first_name, lastname, etc.  

Invalid Identifier: 1A,  int, void, sum-is,   first name, etc.

Data Type in C

         Data type can be represented in variety of ways in any programming language, so that we can store data in system. It determines what types of data should be stored. There are two types of data type in C which are:

         a.      Primary data type   and  

         b.      Secondary data type.

Primary data type

         It is the fundamental data types used to build other data types. The fundamental data types are given below:

        

Variable type	Keyword	Bytes	Range
Character	Char	1	-128 to 127
Unsigned character	Unsigned char	1	0 to 255
Integer	Int	2	-32768 to 32767
Short integer	Short int	2	-32768 to 32767
Long integer	Long int	4	-2147483648 to ….647
Unsigned integer	Unsigned int	2	0 to 65535
Unsigned short integer	Unsigned short int	2	0 to 65535
Unsigned long integer	Unsigned long int	4	0 to 4294967295
Float	Float	4	1.2E-38 to
Double	Double	8	2.2e-308 to
Long double	Long double	10	3.4E-4932 to …

Secondary Data type

a.  Arrays   b.  Pointers     c.  Structure (we will study letter)

Variable

         A variable is a location of a computer's memory used to store data value using unique name and can be changed during program execution time. Any variable declared in a program should confirm to the following:

a.   They must always begin with a letter, although some systems permit underscore as the first character.

 b.   The length of a variable must not be more than 8 characters.

 c.   White space is not allowed.

 d.      A variable should not be a keyword.

 e.      It should not contain any special characters.

Valid Variables:

Sum1,   numb,  Salary,  emp_name,  average1, etc.

Invalid variables:

123,  (area),  6^th ,   %ans,  first name

Types of variable:

1.      Numeric Variable: The variable which stores numeric data only called numeric variable. It may be whole number or fractional number.

         Ex.  Int Salary       float average

2.      String variable: The variable which stores character data only is called string variable. It may be character or string. 

         Ex. Char name,  char w

Constant

         A constant is the fixed values that do not change during the execution of a program. C supports four types of constants. They are character, string, integer and floating point constants.

Types of constant are :

a.  Character constant:  Character constant is a single character which is enclosed with singe quotation mark.  Eg. 'a' ,  'A', '4' , etc.

b.   String constant: String constant of any number of consecutive characters enclosed in double quotation marks whose maximum length is 255 characters. Eg. "it's very easy language", "2*3/5(55-2)", "3400", etc.

c.   Integer constant: An integer constant refers to a sequence of digits that will be either positive or negative. There are three types of integers namely, decimal, octal and hexadecimal.

i.  Decimal integer constant: A decimal constant may have the combination of the digits from 0 to 9 and –ve or +ve sign. Eg. 123,  -56, 0, etc.

ii.  Octal integer constant: An octal integer constant can consist of the combination of the digits 0 to 7 with a leading 0. eg.  0, 01, 0675, etc.

iii. Hexadecimal integer constant: A hexadecimal integer should begin with 0x and it contains the digits from 0 to 9 and an alphabet A to F. eg. 0x2, 0xgf, etc.

d.  Floating point constant: A floating point constant is a base 10 number that contains either a decimal point or an exponent or both. 0, 33, 1.345E+4, 4.22e78, etc.

`

Escape sequence

The non printing characters started with slash ( \ ) which uses special characters with output functions. These are listed below:

Escape sequence         Meaning

         \a                        Audible alert

         \b                        Backspace

         \n                        New line

         \t                         Horizontal tab

         \v                        Vertical tab

         \'                         Single quote

         \"                         Double quote

         \?                        Question mark

Statement

Statement causes the computer to carry out some action as per given instructions. It is terminated by semicolon ( ; ). The types of statement are given below:

a.      Expression statement

         It consists of an expression followed by a semicolon only.

         Example:

         B = 5;

         C = d+e;

         Printf(Enter a number");

b.      Compound statement

         A compound statement consists of several individual statements enclosed with a pair of braces {    }. It provides capability for embedding statements with in other statements.

         Example:

         {

         A = l*b

         Area = 3.14*r*r

         }

c.      Control statement

         A control statements are used to create special program features such as logical tests, loops, branches and it also contains other statements.

         Example:

         For(i=1;i<=100;i++)

Operator

An operator is a symbol which is used to do mathematical or logical operation on data and variables. C has a rich set of operators which can be classified as follows:

a.  Arithmetic Operators

         Those symbols which are used in C – Language to perform simple arithmetic operation such as addition, subtraction, multiplication, division, etc. is called arithmetic operators. It uses two operands so that is called binary operator also.

      Operator        Meaning                      Example

        +           addition                  a+b             2+3=5

         -           subtraction             a-b              5-1=4

         *         multiplication          a*b              2*3=6

         /         division                    a/b               6/2=3

        %        modulus                       a%b             3%2 = 1

b.  Relational operator

         It is required to compare the relationship between operands and bring out a decision and program accordingly. It is also called comparison operator because it is used to compare any two expressions. C supports the following relational operator:

          Operator                 Meaning                                     Examples

               <                   less than                                              a

               <=                 is less than or equal to                        a<=b

               >                   greater than                                         a>b

               >=                 is greater than or equal to                   a>=b

               = =                is equal to                                            a= =b

               !=                  is not equal to                                      a ! = b

c.  Logical operator

         Logical operators are used to give logical value either true of false. C has following logical operators:

         Operator                  Meaning                  Examples

               &&        Logical                   And        (a>b)&&(a>c)

               ||           Logical                     Or          (a>b)||(a>c)      

               !             Logical                  NOT        !(a==b)

 Logical AND (&&)

         This operator is used to operate 2 condition or expression with relational operators if both expression are true then displays true otherwise false.

         Example: a>b && x ==10

 Logical OR (||)

         the logical OR is used to combine 2 expression or the condition evaluates to true if any one of the 2 expression is true.

         Example: a

Logical NOT ( ! )

         The logical not operator takes single expression and evaluates to true if the expression is false and evaluates to false if the expression is true.

         Example: ! (x>=y)

 Assignment Operator

         It is used to evaluate t an expression on the right of the expression  and substitutes it to the value or variable on the left of the expression. It is used to assign value of an expression into variable.

         variable = expression

         Example: x = a+b

Shorthand operator

         It is the combination of arithmetic and assignment so it first performs arithmetic and then only assignment operation.  

operator         shortened operator    assignment

                                                           operator

    +=                    a+=1                      a=a+1  

    *=                    a*1                         a = a*1

   /=                      a/=b                         a = a/b

 %=                    a%=b                        a=a%b

Unary Operator

The increment and decrement operators are one of the unary operations which are very useful in C language. The are extensively used in For  and While loops.

Syntax:

++ variable name (prefix)

variable name ++ (postfix)

- - variable name (prefix)

variable name - - (postfix)

The increment operator + + adds the value 1 to the current value of operand and decrement operator - - subtract 1 to the current value of operand.

Example:

suppose

m = 5;

y = ++m;

in this case  y = m + 1 = 5+1 = 6

                    m = m + 1 = 5 + 1 = 6

again if we rewrite the above as

m = 5;

y = m++;

here, first  ' m ' is assign to y so y = 5  and m = m + 1 =5 +1=6

Relational Operator

The operator which compare two quantities and depending on their relation and take certain decisions.

These comparisons can be done with the help of relational operators. Example: <, <=, >, >=, ==, != (not equals to).

Special Operator

a. Comma operator: It is used to separate expressions when multiple expressions are used in one statement. It always is evaluated left to right and value of the left expression is descarded.

Example: j = (p = 3, p+2);  ( where p+2 = 3+2=5 and p is discarded.

b. Size of Operator: It gives the byte size of data type or variable.

         example:

         int sum;

         m = sizeof(sum);

         n = sizeof(int);

c.  Pointer operator:  * operator is also used for multiplication but when used with a pointer variable, It is used to get the content of the address pointed by a pointer variable to a particular memory location.

Format Specifiers in C

         It tells what type of the data is being processed. The syntax of format specifier is as follows:

         %c  - specify a character              %d   - specify a decimal integer

         %s  - specify a string                    %f     - specify a float

         These format specifier is used with printf ( ) and scanf( ).

         scanf("%d", &a ); asks the user to input an integer and stores it in a.

         printf("the sum of %d and %d is %d",a ,b, sum);

Basic structure of C programs:

Documentation section

Header file inclusion section

Global declaration section of user defined function

main ( ) function section

{

.......................................

.......................................

}

Sub program section

function 1

function 2

...................................

...................................

function n

Syntax for the header file:

#include

(where # include is a pre processor statement.

Header files	Uses
stdio.h	printf(), scanf(), getchar(), putchar(), gets(), puts(), getc(), putc(), fopen(), fclose(), feof()
conio.h	clrscr(), getch()
ctype.h	toupper(), tolower(), isalpha()
math.h	pow(), sqrt(), cost(), tan(), sin(), log()
stdlib.h	rand(), srand(), exit()
string.h	strlen(), strcpy(), strcmp(), strcat(), strlwr(), strupr(), strrev()

Functions:

Formatted I/O

a. Printf(): it is widely used output function. The text which is needed to be shown as output in the screen is shown by the help of printf() function.

         syntax:

         printf(control string, arg1, arg2, ..............);

         ex.       printf("hellow, friend");

               printf("\nThe total amount =Rs. %f",ta);

               printf("enter any number");

b   Scanf(): It is the most frequently used input function.

         syntax:

         scanf(control string, arg1, arg2, ................);

         Example:           

         printf("enter any number");

         scanf("%d", &a);

        

         printf("enter any character and string");

         scanf("%c %s", &w, wo);

Unformatted I/O

a.   getchar(): it accept a character only as an input at a time.

b.   putchar(): it displays just a character on the screen.

c.   gets(): it accepts a string from the user which may have space in between.

puts(): it displays string on the output device.

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