Data Types and Variables in ‘C’ language

Basic structure of C programming To write a C program, we first create functions and then put them together. A C

program may contain one or more sections. They are illustrated below.

Documentation sectionLink sectionDefinition sectionGlobal declaration sectionmain () Function section{

Declaration partExecutable part

}

Subprogram sectionFunction 1Function 2…………..…………..Function n (User defined functions)

Programming Rules

Each instruction should be written in separate statement. A complete C program consists of set of instructions.

The statements in program must be written in sequencial order to get desired output. Unless any logic problem can arises.

All statement should written in small case letters. C has no particular rules for position at which

statement is to be typed. In C program every statement must end with ;

(semicolon). It act as a terminator.

Rules for CommentØ Comment in the program should be enclosed within /* .. */ .Look example below the first line

is comment. For ex. /*This my first program*/ #include<stdio.h> main() { Statement; }

Ø Though comments are not necessary, but it good practice to begin program with comment indicatingpurposeof program so that other person can get idea of program.

Ø You can write any number comment at any place in program mentioning the purpose of the statement.

Ø Use few Comment instead of too many. Ø A comment cannot be nested. For ex., /* The/* first/*program*/*/*/. Ø A comment can split over more than one line. For ex. /*THE First Program*/

Main Method

main() is a collection of the set of statements. Statements that belongs to main() are always written within pairs of {} (opening and closing braces). For ex.

void main() { 1st statement; 2nd statement; } Technically main() is a function because every function has

the pair of parentheses ( ) associated with it. The function in c have their return type. Similarly, if we want

that main() function should not return any value of particular type precede it with void. In case of returning a integer use int.

Declaration

Any variable used in the program must be declared before using it. For ex,

int a,b,c; /*declaration*/ float a,b,c; /*declaration*/ a=a+b; /*usage*/

Variable types

Datatype number Declaration format string

Integer 1,+5,-5 int a; "%d", aFloat 11.363,+1.14,-12.11 float a; "%f", a

Double +1.123123,-1.234345 double a; "%l", a Character 'A','B' char a; "%c",a String "Dev.com" char a[20]; "%c",a

a) While declaration you can also initialize it as

int a=1, b=24; , float a=1.5, b=1.98+3.8*2.7;

b) The order of declaration sometimes matter in initialization.For ex.int i = 1, j=24; is same as int j=24, i=1;

float a=1.8, b= 3.1+a;

This statement is alright but float b=3.1+a, a=1.8; is not the way, we have to initialize a before.

c) Lets see another statements:

int x,y,z; x=y=z=10; work perfectly int x=y=z=10; does not work

we are trying to use y (assign to y) before defining it.

Variable types

Character set are the set of alphabets, letters and some special characters that are valid in C language.

Alphabets: Uppercase: A B C .................................... X Y Z Lowercase: a b c ...................................... x y z

Digits: 0 1 2 3 4 5 6 8 9

Special Characters in C language , <> . _ () ; $ : % [] # ? ‘ & {} “ ^ ! * / | - \ ~

White space Characters: blank space, new line, horizontal tab, carriage return and

form feed

Character Set

Many non-English keyboards do not support all the characters. ANSI C introduces the concept of “Trigraph” sequences to

provide a way to enter certain characters that are not available on some keyboards.

Tri-graph Characters

Keywords Identifiers Constants String Constants Operators Punctuators

Tokens in C

Tokens in C

ØKeywords are C tokens that have a strict meaning.ØThey are explicitly reserved and cannot be redefined.ØANSII C has 32 key words

Keywords

auto do goto signed unsigned

break double if sizeof void

case else int static volatile

char enum long struct while

const extern register switch

continue float return typedef

default for short union

In C programming, identifiers are names given to C entities, such as variables, functions, structures etc. Identifier are created to give unique name to C entities to identify it during the execution of program.

For example:int money;int mango_tree;

Here, money is a identifier which denotes a variable of type integer. Similarly, mango_tree is another identifier, which denotes another variable of type integer.

Identifiers

ØFirst letter must be alphabet (or Underscore)ØAn identif ier can be composed of letters (both

uppercase and lowercase letters) , d ig i t s and underscore '_' only.ØThe first 31 characters of an identifier are significant ØCannot use Keyword as identifiersØMust not contain white space

Rules for Identifiers

ConstantsØConstants in C refers to fixed values that do not

change during the execution of program.ØC supports several types of constants

An integer constant refers to a sequence of digits, There are three types integers, namely, decimal, octal, and hexa decimal. Decimal Constant

Eg: 123,-321 etc.,Note: Embedded spaces, commas and non-digit characters are not permitted between digits. Eg: 15 750, $1000

Octal Constant An octal integer constant consists of any combination of digits from the set 0

through 7, with a leading 0. Eg: 1) 037 2) 0435

Hexadecimal Constant A sequence of digits preceded by 0x or 0X is considered as hexadecimal integer. They

may also include alphabets A through F or a through f.Eg: 1) 0X2 2) 0x9F 3) 0Xbcd

Integer Constants

Program for representation of integer constants on a 16-bit computer.

/*Integer numbers on a 16-bit machine*/main(){

printf(“Integer values\n”);printf(“%d%d%d\n”,32767,32767+1,32767+10);printf(“\n”);printf(“Long integer values\n”);printf(“%ld%ld%ld\n”,32767L,32767L+1L,32767L+10L);

}

OUTPUTInteger values32767 -32768 -32759Long integer values32767 32768 32777

Integer Constants

Certain quantities that vary continuously, such as distances, heights etc., are represented by numbers containing functional parts like 17.548.

Such numbers are called real (or floating point) constants. Eg: 0.0083, -0.75 etc. A real number may also be expressed in exponential or

scientific notation. Eg:215.65 may be written as 2.1565e2 The generic form is mantissa e exponent 2.1565 is called as mantissa and 2 is the exponent Embedded white spaces are not allowed.

Real Constants

A single character constants contains a single character enclosed within a pair of single quote marks.

Eg: ’7’, ‘X’, ‘;’, ' ' Note that character '7' is not same as number 7. Character constants have integer values known as

ASCII values For ex. printf(“%d”, 'A'); will print 65, the

ASCII value of 'A' Similarly, printf(“%c”, 65); will print letter 'A'

Single Character Constants

A string constant is a sequence of characters enclosed in double quotes.

The characters may be letters, numbers, special characters and blank space.

Eg: ”Hello!”, “1987” “?….!”

String Constants

C supports special backslash character constants that are used in output functions.

These character combinations are known as escape sequences.

Backslash Character Constants

A variable is a data name that may be used to store a data value.

It may take different values at different times of execution and may be chosen by the programmer in a meaningful way.

Variable name may consist of letters, digits and underscore character.

Eg: 1) Average, 2) Counter_1 3) Fan1

Variables

They must begin with a letter. Some systems permit underscore as the first character .

ANSI standard recognizes a length of 31 characters. However, the length should not be normally more

than eight characters. Uppercase and lowercase are significant. The variable name should not be a keyword. White space is not allowed.

Rules for Variable Names

Valid Variables Names:John Value T_raiseDelhi x1 ph_value

mark sum1 distance

Invalid Variable Names:123 (area)% 25th

Rules for Variable Names

Storage representation and machine instructions to handle such data differs from machine to machine.

Variety of data type is available in C to select from. A data type is used to

Identify the type of a variable when the variable is declared

Identify the type of the return value of a function Identify the type of a parameter expected by a function

Data Types

ANSI C supports four classes of data types.1. Primary or Fundamental data types.2. User-defined data types.3. Derived data types.4. Empty data set.

Data Types

Primary Data Types

Size and Range Of Data types on 16 bit machine

Data Types - Integer

Data Types - Floating Point

Declarations does two things: It tells the compiler what the variable name it It specifies what type of data the variable will hold

Primary Type Declaration The syntax is

Data-type v1,v2…..vn;Eg:int count;double ratio, total;

Declaration of Variables

C allows user to define an identifier that would represent an existing data type.

The general form is typedef type identifier;

Eg:

typedef int units;

typedef float marks; Another user defined data types is enumerated data type which can be used to

declare variables that can have one of the values enclosed within the braces.

enum identifier {value1,value2,……valuen};

Ex.

enum day {Monday, Tuesday, Wednesday, Thursday, Friday}

enum day week_st, week_end;

week_st = Monday;

User-defined type declaration

Variables in C can have not only data type but also storage class that provides information about their locality and visibility.

/*Example of storage class*/

int m;main(){int i;float bal;…………function1();}function1(){int i;float sum;…………}

Here the variable m is called the global variable. It can be used in all the functions in the program.

The variables bal, sum and i are called local variables. Local variables are visible and meaningful only inside the funct ion in which they are declared.

There are four storage class specifies, namely, auto, static, register and extern

Declaration of Storage Class

Declaration of Storage Class

The syntax is Variable_name=constant

Eg:int a=20;bal=75.84;yes=’x’;

C permits multiple assignments in one line.Example:

initial_value=0;final_value=100;

Assigning Values to Variables

Another way of giving values to variables is to input data through keyboard using the scanf function.

The C library function int scanf(const char *format, ...) reads formatted input from stdin.

The general format of scanf is as follows.

scanf(“control string”, &variable1, &variable2,….);

The ampersand symbol & before each variable name is an operator that specifies the variable name’s address.

Eg:

scanf(“%d”, &number);

Note: printf() and scanf() functions are declared in “stdio.h” header file in C library.

Reading Data from Keyboard

Many times unique constants are required in the program which

are used repeatedly.

For Ex. 3.142, representing value of pi

It is advisable to use named constant or symbolic names rather

than the value like Area = PI * r *r; rather than Area =

3.142 * r *r;

It also increases understandability of the program

Ex. # define PI 3.14159

Ex. # define PASS_MARKS 40

Symbolic names are constants and not variables. They do not

appear in declaration.

Symbolic Constants

Symbolic names have same form as variable names No space between # and define keyword # must be first character in the line Blank space between #define and symbolic name and the

constant No semicolon to end the statement After definition, no value can be assigned to symbolic

constant in the program No data types #define statement may appear anywhere in the program

but before its usage. However usual practice is to place them in the beginning of the program.

Symbolic Constants - Rules

Valid symbolic constant definition#define Students 70#define COURSE BTECH

Invalid symbolic constant definition#define Students = 70# define COURSE BTECH#define COUNT 70;#define A 10, B20#Define Total 100#define amount$ 1000

Symbolic Constants

Certain variables may be required to remain

constant throughout the program execution.

Can be declared as constant

Ex. const int class_size=40;

This tells the compiler that the value of the int

variable class_size must not be modified by the

program.

Variable as Constant

By declaring a variable as volatile, its value may be changed at any time by some external source.

Eg:volatile int date;

The value of a volatile variable may be changed by some external factors even if it does not appear on the LHS of an assignment statement.

The value of a volatile variable can be modified by by its own program as well.

If the value should not be modified by the program while it can be altered by external process, declare as both const and volatile

Ex. volatile const int location = 100;

Variable as Volatile

Problem of data overf low occurs when value of a variable is either too big or too small for data type to hold

Floating point values are rounded to the number of significant digits allowed

Integers are always exact within the limit of the range of the integral data type

C does not provide any warning or indication of integer overflow

Exercise greater care in defining the variable with correct data type

Overflow and Underflow of Data