Question

Write a java program to accept a telephone number with any number of letters. The output should display a hyphen after first 3 digits and subsequently a hyphen (-) after very four digits. Also, modify the program to process as many telephone numbers as the user wants

code optimization: no unnecessary variables , if statements and counters

sample output screen shown with 3 cases(atleast one with blank spaces ect.)Descriptive block and inline comments include.

Answer 1

For single phone no.:

import java.util.*;
public class Telephone {
    public static void main(String[] args) {
        String phoneNo; //To read the telephone no.
        //mark stores the mark where a hyphen will be placed
        //count is a counter that counts the no. of characters passed
   int i, mark = 3, count = 0;
        Scanner sc = new Scanner(System.in);
   System.out.print("Enter a telephone number: ");
   phoneNo = sc.nextLine();
        System.out.print("Telephone no. with hyphens: ");
   for(i = 0; i < phoneNo.length(); i++)
   {
            if(Character.isDigit(phoneNo.charAt(i))) //if character is a digit
            {
       System.out.print(phoneNo.charAt(i)); //print no.
                count++; //increase count by 1
                if(count == mark && i != phoneNo.length() - 1){
                    //if count reaches mark and the digit is not the last
                    System.out.print("-");
                    count = 0; //reset count
                    if(mark == 3) //after first three digits, mark changes to 4
                        mark = 4;
                }
            }
   }
        System.out.println();
    }
}

Output:

To modify the program for more than one telephone numbers, we just have to insert the same task in a loop. The code has been given below:

For more than one number:

import java.util.*;
public class Telephone {
    public static void main(String[] args) {
        String phoneNo; //To read the telephone no.
        //mark stores the mark where a hyphen will be placed
        //count is a counter that counts the no. of characters passed
   int i, mark, count, n;
        Scanner sc = new Scanner(System.in);
   System.out.print("How many nos. you want to enter: ");
        n = Integer.parseInt(sc.nextLine());
        while(n > 0){ //Iterating the same task for n times
            System.out.print("Enter a telephone number: ");
            phoneNo = sc.nextLine();
            System.out.print("Telephone no. with hyphens: ");
            count = 0;
            mark = 3;
            for(i = 0; i < phoneNo.length(); i++)
            {
                if(Character.isDigit(phoneNo.charAt(i))) //if character is a digit
                {
                    System.out.print(phoneNo.charAt(i)); //print no.
                    count++; //increase count by 1
                    if(count == mark && i != phoneNo.length() - 1){
                        //if count reaches mark and the digit is not the last
                        System.out.print("-");
                        count = 0; //reset count
                        if(mark == 3) //after first three digits, mark changes to 4
                            mark = 4;
                    }
                }
            }
            System.out.println();
            n--; //Decrementing n
        }
    }
}

Output: