Different between local and global

Answer 1

The scope or the life span. The life span is from the birth (allocation) to death (deallocation).

The life span of a global variable starts when the application is invoked. It dies when the application terminated. During the execution of the application , this global variable is available to any program unit within that application.

The life span of a local variable, well, only locally. "Local" means a component, a method (subroutine), or even within a bracket ({} or BEGIN-END) of a statement.

Outside of that block of codes, that local variable does not exist, hence cannot be accessed or referenced. Also, the same name of that local variable may be declared again in another local area without conflict, nor memory of the previous one.

For languages similar to C:

for (int i = 0; i < 100; i++)

{

// i can be referenced within { }, and within the for() control itself

}

for (int i = -1; i > -200; i--)

{

// this i is different from the i in the previous for-loop

}

Some computer language would allow you to declare a local variable with the same name as the global one (for example, there are global::X and local::X, but the code only refer as X). Most of the computer language would replace X with local::X at compile time, some would replace it with global::X) Some languages may not have the notion of local variables, everything is global, and some would not have the notion of global variable, but would provide a mean to act like one.