How to add commas to a user input number?

I set the to double and want to add commas if the numbers are long enough

example:

double try1;

double try2;

double try3;

cout << "enter number: ";

cin >> try1; //user puts 1000

cout << try1; //want 1,000 to cout

cout << "enter number: ";

cin >> try2; //user puts 10000.55

cout << try2; //want 10,000.55 to cout

cout << "enter number: ";

cin >> try3; //user puts 100

cout << try3; //want 100 to cout