Code:
int
main() {
char op='c'; // create a character called op and initialise it t the letter 'c'.
int x, y; // create to integers for later called x and y
while(op!='e') { // while op isn't 'e' do...
op is just a sentinal variable that gets changed every time the loop runs through. It lets the program know what the user wants to do. When the user types e the loop will break, and the program exits.
As for your other question, main returns an int. Even though this is commonly known by programmers, you should type it because you are defining main. All functions, including main need a return type.