Technology - Computer science
Basics of C Language



Programming in C

Introduction

A Programing Language should be designed to support certain kind of data, such as numbers,characters,strings etc. To get useful output known as information. A program is a set of statements for a specific task, which will be executed in a sequential form. These statements/instructions are formed using certain words and symbols according to the rules known as syntax rules or grammar of the language. Every program must follow accurately the syntax rules supported by the language.


The C Character set

The characters used to form words,numbers and expressions depend upon the computer on which the program runs. The Characters in C are classified in to four categories.

1. Letters-------------> Ex: A to Z and a to z

2. Digits--------------> Ex: All decimal digits 0 to 9

3. White spaces--------> Ex: Blank space, Horizontal tab, Vertical tab, New line, Form feed

4. Special characters--> Ex:, . ; " ' ! | / \ ~ _ $ ? & ^ * - + < > ( ) [ ] { } % # = @


The C Keywords

The C keywords are reserved words by the compiler. All the C keywords have been assigned fixed meaning. The Keywords cannot be used as variable names because they have been assigned fixed jobs. However, few C compilers allow to construct variable names, which exactly coincides with the keywords. It is suggested not to mix up keywords with variable names.
Keywords:

auto-----break-----case----char----const----continue----default----do

double----else-----enum-----extern-------float--------for-----goto----if
int----long----register---return---short---signed----sizeof---static
struct----switch----typedef----union---unsigned---void---volatile----while

In addition to these standard keywords some more like asm,typeof,huge,interrupt,near,etc.

Identifiers

Identifiers are names of variables,functions, and arrays. They are user-defined names, consisting of sequence of letters and digits, with the letters as the first character. Lower case letters are preferred. However, the upper case letters are also permitted. The (_) under score symbol can be used as an identifier.

Examples:1. #define N 10 2. # define a 15

Here 'N' and 'a' are user-defined identifiers

Constants

The Constants in C are applicable to the values, which do not change during the execution of a program. There are several types of constants in C. They are

1. Numeric Constants

2. Character Constants

Numeric Constants

Numeric Constants Classifieds into several categories.They are

* Integer constants

These are the sequence of numbers from 0 to 9 without decimal points or fractional part or any other symbols. It requires minimum two bytes and maximum four bytes. Integer constants could either be positive or negative or maybe zero. The number without a sign is assumed as positive.

Example: 50,70,+80,-15 etc.

* Real constants

Real constants often as floating point constants. Integer constants are unfit to represent many quantities. Many parameters or quantities are defined not only in integers but also in real numbers. For example length, height, prize, distance etc. are measured in real numbers.

Example: 1.0,2.3450,3.14 etc.

The real constants can be written in exponential notation,which contains a fractional part and an exponential part. For example, the value 2456.123 can be written as 2.4561Xe+3.

The General format of the real number contains mantissa and an exponent. The mantissa is either a real number represented in decimal or an integer.The exponent is an integer number which may be positive or nagative. The letter 'e' separating the mantissa and exponent can be written in lower case or upper case.

Character Constants

* Single character constants:

A characteer constant is a single character. They are also represented with a single digit or a single special symbol or white space enclosed within a pair of single quote marks.

Example: 'a','d','m',etc.

* String constants:

String constants are sequence of characters enclosed within a double quote
marks. The string may be a combination of all kinds of symbols.

Example: "Hello","Sample","Ramana" etc.

Variables

A variable is a data name used for storing a data value. A variable is a name which is used for storing some value in it. Its value may be changed during the program execution of a program. A variable name may be declared based on the meaning of the operation.

Example: height,weight, average, sum, mul etc.

Rules for defining variables

1. They must begin with a character without spaces but underscore is permitted.

2. The length of the variable varies from compiler to compiler. Generally most of the compilers support 8 characters excluding extension. However, the ANSI standard recognizes the maximum length of a variable upto 31 characters.

3. The variable should not be a C keyword.

4. The variable names may be a combination of upper and lower characters. For example Sum and sum are not the same.

5. The variable name should not start with a digit.

Data Types

All C compilers support a variety of data types. This enables the programmer to select the appropriate data type as per the need of the application. Which type of data is storing in a variable is known as data type. Generally data is represented using numbers or characters. The numbers may be integers or real.

A C language programmer has to tell the system before-hand, the type of numbers or characters he is using in his program. These are data types. There are many data types in C language. A C programmer has to use appropriate data type as per his requirement.

C language data types can be broadly classified as

* Primary data type

* Derived data type

* User-defined data type

All C Compilers accept the following fundamental data types

1. Integer -------------------------------------> int

2. Character ----------------------------------> char

3. Floating Point ------------------------------> float

4. Double precision floating point------------> double

5. Void ---------------------------------------> void

The size and range of each data type is given in the below

* char -----------------------------------> -128 to 127

* int -----------------------------------> -32768 to +32767

* float ---------------------------------->3.4 e-38 to 3.4 e+38

* double --------------------------------> 1.7 e-308 to 1.7 e+308

Integer Type :

Integers are whole numbers with a machine dependent range of values. A good programming language as to support the programmer by giving a control on a range of numbers and storage space. C has 3 classes of integer storage namely short int, int and long int. All of these data types have signed and unsigned forms. A short int requires half the space than normal integer values. Unsigned numbers are always positive and consume all the bits for the magnitude of the number. The long and unsigned integers are used to declare a longer range of values.

Floating Point Types :

Floating point number represents a real number with 6 digits precision. Floating point numbers are denoted by the keyword float. When the accuracy of the floating point number is insufficient, we can use the double to define the number. The double is same as float but with longer precision. To extend the precision further we can use long double which consumes 80 bits of memory spaces.

Void Type :

Using void data type, we can specify the type of a function. It is a good practice to avoid functions that does not return any values to the calling function.

Character Type :

A single character can be defined as a defined as a character type of data. Characters are usually stored in 8 bits of internal storage. The qualifier signed or unsigned can be explicitly applied to char. While unsigned characters have values between 0 and 255, signed characters have values from 128 to 127.

Data types and their control strings

Data Type------------------->Size(bytes)--------->Range---------------------------->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 655355............................................... %u

Long................................................ 4 ................................. -2147483648 to 2147483647.................. %ld

Unsigned long............................... 4 ..................................... 0 to 4294967295................................. %lu

Float............................................... 4 .................................... 3.4e-38 to 3.4e+38.................. %f or %g

Double.............................................. 8 ................................... 1.7e-308 to 1.7e+308.......................... %lf

Long Double......................................... 10 .......................... 3.4e-4932 to 1.1e+4932.................. %lf



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