Every programming language has variables. A variable can be defined
as a named storage location whose value can change during the
execution of program .
General declaration syntax is :
data type variable name = [initialization value]
eg int number ; // declaration without initialization
int number = 10 ; // declaration with initialization
- Initialization is optional
- Once declared other parts of program (code) can refer to it by it's name
Scope and Lifetime of a variable
Scope means which part of program can access a previously defined variable.
Normally, scope is defined by curly braces. We will explain scope rules with the help
of following examples.
Consider a for loop and a function
for ( int count = 0 ; count <>{
int i = 5 ;
System.out.println ("Value of i is : " + i ) ; // prints on console
}
void other ( )
{
System.out.println ("Value of i is : " + i ) ; // results in compile time error
}
As variable i is defined inside the for loop, enclosed in the braces it can be used
only there.Trying to use it anywhere else would result in compile time error
Variables declared inside ( ) can also be accessed within the following braces.
In the for loop above, variable count has been declared inside the ( ) and can be
accessed only inside the for loop .
Nested scopes
It is possible to embed another block defined by { } inside another block
Lets look at an example on how scope rule works when there are nested scopes
for ( int i = 0 ; i <>
{ // start outer
// j is not visible (accessible here)
for ( int j = 0 ; j <>
{ // start inner
// i is accessible here
} // end inner
} // end outer
Lifetime : As soon as a variable goes out of scope, it's value is destroyed because it can not
be used after it goes out of scope
for ( int i = 0 ; i <>
{
int x = 10 ;
x = x * 5 ;
System.out.println (" Value of x is : " + x) ;
}
Output is :
Value of x is : 50
Value of x is : 50
Value of x is : 50
This is because every time, next iteration of for loop occurs x goes
out of scope ( as code execution moves out of { } ) . So it's value gets destroyed.
It again gets initialized to 10 when the loop is entered .
Next we will be discussing about Arrays
