What is the use n application of Static variables in C?

Answer 1

When you want a variable that is only initialized once for a function that is called multiple times.

Answer 2

Lets say that you have a function that gets executed every time an even triggers.. (ej. a 1s timer callback)

If you want to increment a minute counter, you have to count how many times the function gets executed...

This may be implemented with a global variable:

int seconds = 0; // global for counting seconds
int minutes = 0;

void timer_callback(){
seconds++;
if (seconds == 60) {
seconds = 0;
minutes++;
}
}

int main(){
<some code>
}

If you want to make "seconds" local (because globals are evil :P ), but you need seconds to keep it's value -like a global do- you can declare as static (inside the function):

int minutes = 0;

void timer_callback(){
static int seconds = 0; // seconds is static

seconds++;
if (seconds == 60) {
seconds = 0;
minutes++;
}
}

int main(){
<some code>
}

As "seconds" is static, is local to timer_callback() -so it's "invisible" to the rest of the program- but don't lose it's value when function ends...

Note: It gets initialized (in this example to 0) ONLY the first time the function is called...

Hope that this example helps you... :)