[I'm new here] What is the error ?

Question

#include <iostream>
using namespace std

int a = 0;
while (a < 10)
{
cout <<"a : "<<a <<endl;
a++;
}

i know thats a noob program, but I really try to understand
And what is the utility of "int main ()" ?

Answer 1

int main() is the starting of program

when compiler compiles your program it finds for the int main()