register int a;
Register variables are similar to automatic variable and exists inside that particular function only.
If the compiler encounters register variable, it tries to store variable in microprocessor's register rather than memory. Value stored in register are much faster than that of memory.
In case of larger program, variables that are used in loops and function parameters are declared register variables.
Since, there are limited number of register in processor and if it couldn't store the variable in register, it will automatically store it in memory.
Static Storage Class
The value of static variable persists until the end of the program. A variable can be declared static using keyword: static. For example: static int i;
Here, i is a static variable.
Example to demonstrate the static variable
#include <stdio.h>
void Check();
int main(){
Check();
Check();
Check();
}
void Check(){
static int c=0;
printf("%d\t",c);
c+=5;
}