C programming. Please explain. I will rate like.

I // Fig. 3.6: fig03_06.0 2 // Class average program with counter-controlled iteration #include 4 5 // function main begins program execution 6 int main( void ) 7 [ unsigned int counter; // number of grade to be entered next 9 int grade; // grade value 10 int total; // sum of grades entered by user int average; // average of grades // initialization phase total = 0; // initialize total counter = 1; // initialize loop counter 16 17 // processing phase 18 while (counter