Lesson # 2 Variable and data types

LESSON  # 2

VARIABLE AND DATA TYPES

Variables and data types are building blocks of C++. A variable is a container which stores different data types. Data types determine that what kind of data (value) can be stored in a variable. There are several data types in C++  such as: Numeric (5585, 953.52) can be an integer, unsigned integer, double or  float.
INTEGER	An integer is whole number without decimal point e.g. 5585. In C++ keyword int is used to declare an integer. An integer can hold a number that contains 4 bytes i.e. -2000000000  to + 2000000000. For storing 8 bytes number we use unsigned int but unsigned int only store positive numbers.
DOUBLE	Double holds a number with decimal point e.g. 953.52. It can store a number with 8 bytes.  Keyword double is used to declare a double. We can also use float which only takes a number of 4 bytes. In C++, to check size of a data type, we use sizeof(data type) function. For example, cout<<sizeof(int) returns the size of int.
STRING	String is zero or more characters enclosed in double quotes. For example “Hello world” is string because it has been enclosed in double quotes “ ”. Keyword string is used to declare a string.
CHARACTER	Character is single letter enclosed in single quotes e.g ‘d’ is a character. To declare a character, the keyword  char is used.   ( single letter e.g. ‘d’ , ‘y’) . Remember that these values are stored as numbers which based on ASCII code.
BOOLEAN	Boolean holds true or false and is declared with keyword bool.

RULES FOR NAMING VARIABLES:

Must begin with a letter May consist of letters, numbers, letter and underscore No space between

Good example:              Name, last_name; a2z             Bad example:               first name; 4family

Let illustrate these ideas with help of an example:

C++ Code	Explanation
using namespace std; #include<iostream> main() {
int a;	Declaring an integer variable with name a
a=5585;	Assigning (storing) the data 5585 into variable a
double b;	Declaring a double variable with name b
b=953.52;	Assigning (storing) the data 953.52 in into variable b
string c;	Declaring a string variable with name c
c="Hello world";	Assigning (storing) the text data hello world in into variable c
char d;	Declaring a char variable with name d
d='d';	Assigning (storing) the data d in into variable d
cout<<a<<"\t"<<b<<"\t"<<c<<"\t"<<d<<"\n";	Displays all variables on the screen, note we are putting all variable together by inserting << after each variable and a tab \t character after variable. At end \n is for next line.
system("pause"); }
Output
5585    953.52  Hello world     d Press any key to continue . . .
CLICK HERE TO DOWNLOAD SOURCE CODE

CODE IN ACTION 

Let’s do one more example:

C++ Code	Explanation
using namespace std; #include<iostream> main() {
int x,y,z;	Declaring three int variables i.e. x,y,z. Remember we can declare variables in a single line, in this case all these three variables are of type int.
x=10;	Assigning value
y=15;	Assigning value
z=x+y;	Assigns the values of another two variables. Variable z holds the sum of x and y.
cout<<z;	Displays z on the screen
cout<<y-x;	Displays the result of y – z, note that we can also do simple arithmetic operations with variables.
cout<<"\n";	Moves the cursor to next line
double a=5.5,b=4.5,c=a*b;	Declaration and initialization (assigning values ) at the same time, it does not matter as far as we are dealing with a single data type.
cout<<c;	Displays c on the screen
cout<<"\n";
cout<<sizeof(int);	sizeof() functions returns the size of int
cout<<"\n";
system("pause"); }
Output
255 24.75 5345.654 Press any key to continue . . .
CLICK HERE TO DOWNLOAD SOURCE CODE

CODE IN ACTION