====== Variable Scope   ======

Variables in the C programming language, which Arduino uses, have a property called ''scope''. This is in contrast to languages such as BASIC where every variable is a ''global'' variable.

A global variable is one that can be ''seen'' by every function in a program. Local variables are only visible to the function in which they are declared. In the Arduino environment, any  variable declared outside of a function (e.g. setup(), loop(), etc. ), is a global variable.

When programs start to get larger and more complex, local variables are a useful way to insure that only one function has access to its own variables. This prevents programming errors when one function inadvertently modifies variables used by another function.

It is also sometimes handy to declare and initialize a variable inside a ''for'' loop. This creates a variable that can only be accessed from inside the for-loop brackets.

==== Example:   ====
<code arduino>int gPWMval;  // any function will see this variable

void setup()
{
  // ...
}

void loop()
{
  int i;    // "i" is only "visible" inside of "loop"
  float f;  // "f" is only "visible" inside of "loop"
  // ...

  for (int j = 0; j <100; j++){
  // variable j can only be accessed inside the for-loop brackets
  }

}</code>
Source: arduino.cc