This file adds commas in the US style to user-entered numbers. Stanford CS106a assignment 4.1

Insert commas in long numbers

/** This class adds commas in the US style to user-entered numbers
 * @author Lisa Stephens February 6, 2014
 * Complete
 * written as a response to Stanford CS 106a exercise 4.1
 * The run() method was essentially given by the assignment.
 */
import acm.program.ConsoleProgram;

public class AddCommas extends ConsoleProgram{

	
	public void run(){
		while (true) {
			String digits = readLine("Enter a numeric string: ");
			if (digits.length() == 0 ) {
				println("Done");
				break;
			}
			println(addCommasToNumericDigits(digits) );
		}
	}

	private String addCommasToNumericDigits(String number) {
		// Working backward from the digits in the string, build the new string, adding
		// commas when appropriate
		String newNumberWithCommas = "";
		
		for (int i = 0; i< number.length(); i++) {
			char ch = ( number.charAt(number.length() - 1 - i) );
			newNumberWithCommas = ch + newNumberWithCommas;
			if ( ( ( (i+1) % 3) == 0 ) && ( (i+1) < number.length())  ) {
				newNumberWithCommas = "," + newNumberWithCommas;
			}
		}
		return newNumberWithCommas;
	}
}