Trying to check command line for bad input with while loop so if wrong it will reprompt questions

Posted on 2004-09-08
Last Modified: 2012-06-27
Hello, i hope this is an easy fix here is my problem..........

I'm trying to use the commandline to prompt the user for two things the degree of polynomial and its coefficients as follows but if it makes any error i want to reprompt the questions untill they answer correctly.I'll do this with a while true loop and 2 if statements if the two statements not entered flag will be false exit while loop continue calculation

enter degree:
enter coeff with spaces betwwen each ex 1 2 3:

then i'll use string tokenizer to get each coeeficient and place into an array. My problem is io need to make sure when they enter a degree these two cases are followed countTokens is number of coeff

1) if (degree < countTokens() ) thedn reprompt questions because degree was smallerthan the amount of coeff

2) if(degree +2 <=  countTokens() this would mean the array[degree+1] would give out of boundry exception because more coefficients than array allots

does this logic make sense?  so example input output

enter degree:3
coeff :1 2
so this would re ask question

enter degree:3
coeff: 1 2 3 4 5
reask question

enter deg:3
coef 1 2 3 4
ok ! this will break the loop.

so here is my code please any help will be greatly appreciated i can't get it to only respond when appriate datra is answered to stop array exceptions.


boolean poly_flag=true;


                        System.out.println("Enter in degree of polynomial : ");
                        main.setDegree( Integer.parseInt(buffer.readLine()) );             //grab degree from user input

                      System.out.println("Enter in non negative coefficients n for example 1 2 3 will be 1x^2 + 2x + 3");
                    coef_input = buffer.readLine();                            //grab coefficients from user input

                      coef = new int[main.getDegree() +1];    // allocate array size of degree plus one

                       token = new StringTokenizer(coef_input); //Use stringtokenizer to truncate coefficients

               int deg = main.getDegree();
                // check to make sure coefficients do not exceed array or are smallr than degree
                if( deg >=  token.countTokens() )
                    System.out.println("Your degree is bigger than the amount of coefficients please try again");

                  }//end while loop
Question by:tyweed420
LVL 86

Expert Comment

Comment Utility
>>because more coefficients than array allots

Any particular reason why you should limit this?

Author Comment

Comment Utility
because i use degree +1 to allocate the array., so if thery enter more coef than array allows its wrong for the polynomial and it creates out of bounds exceptionm

is this not correct thinking

Accepted Solution

jLasitha earned 50 total points
Comment Utility
This may be the code that you want...

import java.util.*;

public class Polynomial {
    private static String read()throws Exception{
        BufferedReader br = new BufferedReader( new InputStreamReader( ) );
        return br.readLine();

    public static void main(String[] args) {
        int[] aCoeff;
                System.out.print("Enter degree :");
                int degree = Integer.parseInt( read() );
                System.out.print("Enter coeff:");
                String coeff =   read();
                StringTokenizer st = new StringTokenizer( coeff );
                int noOfCoeff = st.countTokens();
                if( ( degree + 1 ) ==  noOfCoeff ){
                    System.out.println("Ok! Break loop");
                    aCoeff = new int[ noOfCoeff ];
                    //Copy elements to the array
            }catch( Exception e ){
                System.out.print( e.getMessage() );

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