I am new to the forums so first of all I'd like to say "Hi"! I'm new to Java programming and am trying to make a simple payroll calculating program with three while loops.
The first while loop keeps the program going until the user enters the sentinel "stop". The second and third loops are error traps that ensure the user enters a positive number before continuing.
For some reason, the while loops are not working and I have tried every variation I can think of. The program runs just fine, it just ignores the while loops. If someone could provide some suggestions as to what I'm doing wrong, I'd really appreciate it.
I'm using NetBeans 8.0 IDE if that helps.
Here is my code:
Import java.util.*;
Import java.text.*;
public class PayrollProgramVersion2
{
//begin main program
public static void main(String[] args)
{
//declare new scanner
Scanner sc = new Scanner (System.in); // declare new scanner object
DecimalFormat Dollars = new DecimalFormat ("$0.00"); //format for dollars
String Employee; //employee's name
Double Hours, //hours worked
Rate, //pay rate
Pay; // Hours * Rate
Boolean Continue = true; // sentinel for program loop
//welcome user, prompt for employee name, and assign input to Employee
System.out.println ("Welcome to the payroll program!");
System.out.println ("What is the employee's name? (Enter stop to quit.)");
Employee = sc.nextLine();
// while loop continues program until user enters "stop"
while (Continue == true)
{
if (Employee.equalsIgnoreCase("stop"))
{
Continue = false;
} // end if
else
{
//prompt for hours worked and assign to Hours
System.out.println ("How many hours did " +Employee+ " work?");
Hours = sc.nextDouble();
//this block is an error trap to ensure input is positive before continuing
while (Hours < 0)
{
System.out.println( "Error - input must be a positive number");
System.out.println ("How many hours did " +Employee+ " work?");
Hours = sc.nextDouble();
}
//prompt for pay rate and assign to Rate
System.out.println( "How much does " +Employee+ " make per hour?");
Rate = sc.nextDouble();
//this block is an error trap to ensure input is positive before continuing
while (Rate < 0)
{
System.out.println( "Error - input must be a positive number");
System.out.println( "How much does " +Employee+ " make per hour?");
Rate = sc.nextDouble();
}
Pay = Hours * Rate; // calculate payrate
//display results
System.out.println(Employee+ "'s paycheck is " +(Dollars.format(Pay))+ ".");
System.out.println ("What is the employee's name? (Enter stop to quit.)");
Employee = sc.nextLine();
} //end else
} //end while
System.out.println ("Thank you for using the payroll program. Goodbye!");
} // end main
} // end program
From what I can see you should make your while (hours<0) to while (hours<0 || hours == null).
This is because... As far as I can see you initialise hours. But no value is input into it. So it remains as null. You could also try changing the while to an if.
Hope this helps. It may be that it does default to 0 but it may be worth for testin purposes to have a console output.
System.out.println(hours);
Befor the while loop to see what your program is reading hours as.
Hope this helps.
The error is that nextDouble does not eat the newline. It skips newlines at the beginning, so in effect only the last nextDouble is concerned.
Best to make a utility function:
Instead of
Hours = sc.nextDouble();
call your own function:
Hours = nextDouble(sc);
private static double nextDouble(Scanner sc) {
double value = -1.0;
if (sc.hasNextDouble()) {
value = sc.nextDouble();
}
sc.nextLine();
return value;
}
Use a small initial letter for field and method names.
Use double/boolean/int instead of the Double/Boolean/Integer as the latter are Object wrappers (classes); the first primitive types.
Call sc.close(); (for good order).
Aside from what has been said above:
sc.nextDouble consumes and returns the next input from the current line. It does not forward the line.
sc.nextLine consumes and returns the input from the current line and forwards to the next line
At the end of your while loop you call Employee = sc.nextLine(); If you follow your logic and only input allowed values, this will always return an empty string as it consumes the current line where your most previously removed double was stored(now empty string "")
When you do something like:
Hours = sc.nextDouble();
you trust the user to enter a double value, and in case the user entered illegal value, a String for example, this line will throw an exception.
You can solve it like this:
while (Hours < 0)
{
System.out.println( "Error - input must be a positive number");
System.out.println ("How many hours did " +Employee+ " work?");
String hours = sc.nextLine();
try {
Hours = Double.valueOf(hours);
}
catch (NumberFormatException e) {
// keep looping until we get a legal value
Hours = -1.0;
}
}
Related
all!
I'm a university freshman computer science major taking a programming course. While doing a homework question, I got stuck on a certain part of my code. Please be kind, as this is my first semester and we've only been doing Java for 3 weeks.
For context, my assignment is:
"Create a program that will ask the user to enter their name and to enter the number of steps they walked in a day. Then ask them if they want to continue. If the answer is "yes" ask them to enter another number of steps walked. Ask them again if they want to continue. If they type anything besides "yes" you should end the program by telling them "goodbye, [NAME]" and the sum of the number of steps that they have entered."
For the life of me, I can not get the while loop to end. It's ignoring the condition that I (probably in an incorrect way) set.
Can you please help me and tell me what I'm doing wrong?
import java.util.Scanner;
public class StepCounter
{
/**
* #param args the command line arguments
*/
public static void main(String[] args)
{
final String SENTINEL = "No";
String userName = "";
String moreNum = "";
int numStep = 0;
int totalStep = 0;
boolean done = false;
Scanner in = new Scanner(System.in);
Scanner in2 = new Scanner(System.in);
// Prompt for the user's name
System.out.print("Please enter your name: ");
userName = in.nextLine();
while(!done)
{
// Prompt for the number of steps taken
System.out.print("Please enter the number of steps you have taken: ");
// Read the value for the number of steps
numStep = in.nextInt();
// Prompt the user if they want to continue
System.out.print("Would you like to continue? Type Yes/No: ");
// Read if they want to continue
moreNum = in2.nextLine();
// Check for the Sentinel
if(moreNum != SENTINEL)
{
// add the running total of steps to the new value of steps
totalStep += numStep;
}
else
{
done = true;
// display results
System.out.println("Goodbye, " + userName + ". The total number of steps you entered is + " + totalStep + ".");
}
}
}
}
To compare the contents of String objects you should use compareTo function.
moreNum.compareTo(SENTINEL) return 0 if they are equal.
== operator is used to check whether they are referring to same object or not.
one more issue with addition of steps, addition should be done in case of "No" entered also
Use
if(!moreNum.equals(SENTINEL))
Instead of
if(moreNum != SENTINEL)
Also, make sure to add: totalStep += numStep; into your else statement so your program will actually add the steps together.
So I'm new to java programming, coming from Python, and there's a few concepts that I can't quite understand.
I'm writing a program which allows the user to enter as many numbers as they want and the program should output the average of all of the numbers. I used a while loop to loop through the inputs by the user as many times as they wanted, but I needed a way of exiting the loop so that the program could proceed with calculating the average of all of the inputs. I decided that if the user enters an "=" sign instead of a number, then the program would break out of the loop, but since the Scanner variable was looking for a double, and the "=" sign is not a number, I would have to make it a String. But because the Scanner is looking for a double, the program threw an error when it encountered the "=".
How can I get the program to exit the loop when the user types "="? I know I could just allow the user to enter a number that breaks the loop, but if it was a real world program and the user entered a number, it would count that number along with the previous ones when calculating the average. The code I have so far is as follows:
import java.util.Scanner;
// imports the Scanner class
public class Average{
public static void main(String[] args){
double num, total = 0, noOfInputs = 0, answer;
Scanner scanner = new Scanner(System.in);
while(true){
System.out.print("Enter number: ");
//Prompts the user to enter a number
num = scanner.nextDouble();
/*Adds the number inputted to the "num" variable. This is the
source of my problem*/
if(num.equals("=")){
break;}
/*The if statement breaks the loop if a certain character is
entered*/
total = total + num;
//Adds the number inputted to the sum of all previous inputs
noOfInputs++;
/*This will be divided by the sum of all of the numbers because
Number of inputs = Number of numbers*/
}
answer = total / noOfInputs;
System.out.print(answer);
}
}
Several ways to do this.
You could read every number as a string, and then if it is a number, parse it to get the value.
Integer.parseInt(String s)
Or you could check what comes next and read accordingly:
while (scanner.hasNext()) {
if (sc.hasNextInt()) {
int a = scanner.nextInt();
} else if (scanner.hasNextLong()) {
//...
}
}
Or you could just catch the InputMismatchException, and work from there.
try{
...
} catch(InputMismatchException e){
//check if '=' ...
}
I'm trying to only accept numbers from a user. This code works for giving them an error message if they enter a letter. But it doesn't work for if they hit Enter or just white space. I've tried initializing a String called test as null and then setting scnr.nextLine() = test, and then checking if test is empty, but I didn't understand how to keep the rest of the program operating correctly when I did that. Scanner is very tricky to me. Please help!
double mainNumber = 0;
System.out.print("Enter a number: ");
if (scnr.hasNextDouble() ){
mainNumber = scnr.nextDouble();
System.out.println(mainNumber);
scnr.nextLine();
}
else {
System.out.println("Sorry, please enter a number.\n");
scnr.nextLine();
}
You have to use while-cycle and loop input as long as needed before user put a valid number.
This code
public static void main(String[] args) {
Scanner scnr = new Scanner(System.in);
double mainNumber = 0;
boolean isValidNumber = false;
System.out.print("Enter a number: ");
while (isValidNumber == false) {
String line = scnr.nextLine();
try {
mainNumber = Double.valueOf(line);
isValidNumber = true;
} catch (NumberFormatException e){
System.out.print("Sorry, please enter a number.\n");
}
}
System.out.println("Main number is: " + mainNumber);
}
Having this sample output :
Enter a number: sdfgsgxb
Sorry, please enter a number.
xcvbxcvb
Sorry, please enter a number.
gsfdfgsdf
Sorry, please enter a number.
aearg
Sorry, please enter a number.
15.77
Main number is: 15.77
Well I guess your code is in a while loop or something ? So that it keep asking until the user enter the right value.
Then you should (for convenience) use String str = scnr.nextString() instead of nextDouble() and analyze the string it returned.
You can use str.trim() to remove whitespaces (and then check if string is empty with str.isEmpty() ), and to check if it's a number you can use regexp ( How to check that a string is parseable to a double? and any regex tutorial you can find ) or just use this regex: str.matches("\\d+") (returns true if str is a number, but no comma here).
Of course, don't forget to cast your String as double after: Double.parseDouble( str.replace(",",".") );. I hope the "replace" part is obvious ;)
You might use the following snippet to read one double value:
Scanner scanner = new Scanner(System.in);
try {
double number = Double.parseDouble(scanner.nextLine());
} catch (NumberFormatException e) {
e.printStackTrace();
}
So this is my code i dont know what to add if i want to display invalid message for the non numeric inputs please help ty
import java.util.Scanner;
public class Date
{
public static void main (String args [])
{
int x;
Scanner in = new Scanner (System.in);
System.out.print("Enter a date ");
x = in.nextInt();
while (x < 1520 || x > 3999)
{
System.out.println ("Invalid Gregorian Calendar date.");
System.out.print ("Please Input a valid Gregorian Calendar date: ");
x = in.nextInt();
}
System.out.println("Good");
Use a try catch block, and put x = in.nextInt(); inside it
I've changed your code a bit. I think this is what you were aiming for.
I'm not that good in explaining but I try to tell what I did.
First of all I got rid of your in.nextInt() since this is very restrictive. It does only accept an integer and will throw an exception if you type something else in. Normally this would be OK, but since you want the user to be able to correct the input, this will cause more troubles than it would solve.
I then put your code into an infinite loop while(true) which assures, you do not have to restart your application again once you've typed in a wrong value.
What is going on within the loop is quite simple. The console prints out what you want the user to do and reads the consoles input as a String, so you don't have to face any exceptions in the first place.
I then try to parse the given String into an integer value. I added trim() to kill leading spaces as well as trailing, so I won't have to deal with users being confused by typing in numbers with a space since they don't directly see whats wrong when getting their "not an integer" error. This would be thrown, if the input contains spaces.
Now I check whether or not the given integer-value fits your specifiation. I don't need a loop here, so I changed it to be a simple if-statement.
If the value is wrong (or lets say the if (x < 1520 || x > 3999) returns true) I'm going to print out your error message. Since we already passed casting the String input into the integer and we do not reach the else-branch we now return back to the beginning of our loop with printing out the request again before waiting for a new input to be made.
Now, as soon as the user typed in another value, e.g. 2011 (which is valid based on your specification) we will now reach the else-branch which prints the "Good" and leaves the loop by calling break. And since there is nothing left to do for the application it will stop running. If you want the user to be able to type in new values in the positive case, you simply have to remove the break-statement.
If the user types in a value which is not an integer, the cast will fail and throw a NumberFormatException. We catch this exception by surrounding the cast with the try-catch-block and print out the integer-error once we've reached the catch-block.
Then the application reacts the same way like if you typed in a wrong number and we will return to the beginning of the loop again.
The reason for putting a try-block around the Scanner is to handle closing.
import java.util.Scanner;
public class Date {
public static void main(String args[]) {
String input = "";
int x = 0;
try (Scanner in = new Scanner(System.in);) {
while (true) {
System.out.print("Please Input a valid Gregorian Calendar date: ");
input = in.nextLine();
try {
x = Integer.parseInt(input.trim());
if (x < 1520 || x > 3999) {
System.out.println("Invalid Gregorian Calendar date.");
}
else {
System.out.println("Good");
break;
}
} catch (NumberFormatException e) {
System.out.println("Given value \"" + input.trim() + "\" is not an integer.");
}
}
}
}
}
The Scanner class has a method for this
Scanner in = new Scanner(System.in);
int x;
if(in.hasNextInt()){
x = in.nextInt();
System.out.println("Valid number");
}else{
System.out.println("Not a number");
}
To keep prompting until a valid number is entered
int x;
System.out.println("Enter a number: ");
while(!in.hasNextInt()){
System.out.println("Invalid number, try again: ");
key.nextLine(); // Flush out invalid number
}
x = key.nextInt();
// Week 3 Checkpoint1: Payroll Program Part 2
// Due May 04, 2012
// Created by: Kennith Adkins
import java.util.Scanner;
public class Assignment1
{
public static void main ( String[] args )
{
Scanner input = new Scanner(System.in);
// Variables
String employeeName = null;
int hours;
double rate;
double pay;
while ( employeeName != "stop")
{
// Request information from user
System.out.print ( "Employee Name: ");
employeeName = input.nextLine();
System.out.print ( "Hourly Rate: ");
rate = input.nextDouble();
System.out.print ( "Number of Hours worked this week: ");
hours = input.nextInt();
// Calculate pay
pay = rate * hours;
// Display information
System.out.printf ("%s will get paid $%.2f this week.\n", employeeName, pay);
}
}
}
When I run the program it runs fine. When it hits the loop and repeats, Employee Name: and Hourly Rate seem to bunch up. Also how would I get it to immediately stop after typing stop as employee Name?
As this appears to be a homework question I'll point you in a learning direction.
So for the employee name question I will redirect you to How do I compare strings in Java?
The scrunching issue is because when you reenter the loop and call scanner(input).nextLine it ends up actually reading the input text that it had not seen yet. So one option is to switch to something else lick a BufferedReader or move the scanner deceleration down in to the loop.
More research
I haven't worked much with the scanner class and after seeing this I was somewhat confused. The issue is actually the nextInt and nextDouble. They dont claim the return charter and as such when you call next line next time it is picking up the leftover return character.
So my option of reseting the scanner when reentering works in this specific case but you should either use 2 scanners or move off of scanners.
Scanner txtinput = new Scanner(System.in);
Scanner numberinput = new Scanner(System.in);