Object Oriented Programming: Part 4

Variables in C++

In any programming we typically do lots of calculations. The result of these calculations is stored in computers memory. Like human memory, the computers memory also consists of cells. The calculated values are stored in these memory cells. To make the retrieval and usage of these values easy these memory cells are given names. Since the value stored in each location may change the names given to these locations are called variable names.

Data Types

When using variable we store the data in computers memory, we need to define its type that is format that what we want to store in. So, that computer can handle the data actions that we will perform after storing. There are following types of data:

(i)     Char (Character)

It is smallest data type in C++. It allocates 1 bytes (8 bits) memory in 32 bits computers to store the char value within the range

(a)  Signed char (-128 to 127)

(b)  Unsigned char (0 to 255)

(ii)   Short

It allocates 2 bytes (16 bits) memory in 32 bits computers to store the values within the range

(a)  Signed short (-32768 to 32767)

(b)  Unsigned short (0 to 65535)

(iii)  Long

It allocates 4 bytes (32 bits) memory in 32 bits computers to store the values within the range

(a)  Signed long (-2147483648 to 2147483647)

(b)  Unsigned long (0 to 4294967295)

(iv) Int (Integer)

It allocates 4 bytes (32 bits) memory in 32 bits computers to store the integer values within the range

(a)  Signed long (-2147483648 to 2147483647)

(b)  Unsigned long (0 to 4294967295)

Note: Only int changes the allocated space as per computer (32 bits or 64 bits computers)

(v)  Float (Floating Point)

It allocates 4 bytes (32 bits) of memory in 32 bits computers to store the floating numbers of 7 digits (excluding decimal).

(vi) Double

It allocates 8 bytes (64 bits) of memory in 32 bits computers to store the floating numbers of 15 digits (excluding decimal).

(vii)     Long Double

It allocates 10 bytes (80 bits) of memory in 32 bits computers to store the floating numbers of 19 digits (excluding decimal).

(viii)    Bool

It is short of Boolean. It can take values in true/false. It allocates 1 byte (8 bits) of memory. This data type is only compatible with ANSI C compilers.

(ix)  wchar_t

It is short of wide character. This data type is designed as to handle the international marked characters. It allocates 2 bytes (16 bits) of memory. This data type is also only compatible with ANSI C compilers.

Declaration of Variables

To use variables in C++ programming language we have to declare it first. To declare any variable first we use its data type name and then write the variable name. Variable name should be communicable and understandable that is variable name can describe its nature and properties. For example, to store student mark we should use std_mark and to store student address use std_add. Variable name cannot consist space and also cannot start with numeric values. Foe example

To declare three variables we can write

          int x, y, z;

instead of writing

          int x;

          int y;

          int z;

Initialisation of variables

It is the process to assign the value in the variable, which is declared we can initialise the value at the time of variable declaration also. For example,

          int x=10;

          OR

          int x;

          x=10;

One another way to declare the variable and initialise the value in it is to use the open and close parenthesis. For example,

          int x(10);

Scope of variables

To use any variable in C++ programming, variable should be declared first. Without declaration of variable we cannot use in program. There are two types of variable scopes.

(i)                 Local Variables

The variable which is declared for local use like in any function, loop or even only in main function is known as local variables.

(ii)               Global Variables

The variable which is declared for global use in program is known as global variables. Global variables can be used anywhere in program and no need to declare everywhere.

Example on scope of variables:

#include<iostream.h>

int sum;                  //global variable

int num1, num2;          //global variable

main()

{

int multi;                 //local variable

multi=num1*num2;

cout<<multi;

}

Constants

It is an expression that has fixed value. They are divided into many categories:

(i)           Integer Numbers

Numbers within the range -2147483648 to 2147483647 are constant integers. The numbers like octal and hexadecimal are also integer constants.

(ii)         Floating Point Numbers

The number which has exponents is known as floating point numbers. For example,

3.14159

6.02e23=6.02*10²³

1.6e-19=1.6*10^-19

(iii)   Character Strings

The numbers which has nun-numerical value is known as string. Strings are always covered with single quote or double quote. For example,

       'z'

       'p'

       "Hellow Guys"

       "Hello, how are you?"

(iv)   Escape Sequence

The character which is only used to work with strings are known as escape sequence. Escape sequences are always used with inverted slash (\). For example,

       Usages of escape sequences:

              printf("Hellow\nhow are you?");

              printf("Are you good\?");

(v)   Defined Constants

For to use any variable global we use the defined constants. Even in another linked file usages the defined constants. For example,

       #define PI 3.14

       #define newline '\n'

       #define height 30

(vi)   Declared Constants

One another way to create any variable constant permanently is to use const prefix before. For example,

       const int height=100;

       const int salary=12000;

Note: Continue in next part.

HAVE A HAPPY CODING!