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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.
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 variables. This prevents programming errors when one function inadvertently modifies variables used by another function.
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"
// ...
}
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