Need Help Creating A Loop!

[christian loran]

my program compiles with no errors though I need help actually getting the program to loop. I want it to loop if yes is entered , and stop if no is entered. How would I go about doing this? can someone please provide the proper code needed? I am very new to Java and I am trying my best to learn. this program is a project from a book I am reading.

here is my code:

/*  Protoype program to be used to prove  first concepts Algorithm project */
 
import java.io.*;
 
import java.lang.*;
 
import java.text.*;
 
import java.util.*;
 
//Set up public class
 
public class  document2
 
{
 
//declare main() method
 
public static void main(String[] args) throws IOException
 
{
 
//Declare data types
 
float length,width,area,circum,loop,yes,no;
 
//set up input stream
 
Scanner  readin = new Scanner(System.in);
 
//prompt for length
 
System.out.println("\n\n enter value for length");
 
//stream in length and convert to float
 
length = readin.nextFloat();
 
//prompt for width
 
System.out.println("\n\n enter value for width");
 
//stream in width and convert to float
 
width = readin.nextFloat();
 
//Calculate results
 
area = length*width;
 
circum = 2* (length + width);
 
//prepare data for out put display
 
 DecimalFormat twodig = new DecimalFormat("########.##");
 
 System.out.print("\n\nThe results of the calcuations are\n\n\n");
 
 System.out.print("the area is:\t\t"  +  twodig.format(area) + "\n\n");
 
 System.out.println("the circumference is:\t\t" + twodig.format(circum));
 
 //prompt for loop
 
 System.out.println("\n\n calculate again YES / NO ?");
 
 //stream in width and convert to float
 
loop = readin.nextFloat();
 
 
 
 }//end main
 
 }//end class

[fred rosenberger]

There are three kinds of loop:

1) a for-loop. This is most commonly used when you know exactly how many times you will need to loop

2) a while-loop. this is used when you may need to loop, or you may not. It is possible the body will NEVER be executed.

3) a do-while loop. This loop body will ALWAYS execute at least once.

There are different philosophies on whether the do-while should ever be used, but it sounds like that would meed your needs.

Basically, you need to surround all the code you want to run over and over again in this:

do
{

} while (condition)

it looks to me like you'd want to put everything from line 33 to 69 inside the body. Then, you need to establish your condition for terminating the loop. You probably want to test to see if some input is equal to 'yes' or 'no', depending on how you word the question.

Why don't you give it a try, and show us what you come up with?

[christian loran]

This is my valient effort at trying to get it to actually work, though it was a failure unfortunately. Here is my code

/*  Protoype program to be used to prove  first concepts Algorithm project */

import java.io.*;

import java.lang.*;

import java.text.*;

import java.util.*;

//Set up public class

public class  document2

{

//declare main() method

public static void main(String[] args) throws IOException

{

//Declare data types

float length,width,area,circum,loop;

boolean yes,no;

//set up input stream

Scanner  readin = new Scanner(System.in);

//prompt for length

int yes;
do
{

System.out.println("\n\n enter value for length");

//stream in length and convert to float

length = readin.nextFloat();

//prompt for width

System.out.println("\n\n enter value for width");

//stream in width and convert to float

width = readin.nextFloat();

//Calculate results

area = length*width;

circum = 2* (length + width);

//prepare data for out put display

 DecimalFormat twodig = new DecimalFormat("########.##");

 System.out.print("\n\nThe results of the calcuations are\n\n\n");

 System.out.print("the area is:\t\t"  +  twodig.format(area) + "\n\n");

 System.out.println("the circumference is:\t\t" + twodig.format(circum));

 //prompt for loop

 System.out.println("\n\n calculate again YES / NO ?");

 //stream in width and convert to float

 } while (yes);


loop = readin.nextFloat();



 }//end main

 }//end class

and this was the error message!

C:\Users\christian\Desktop\document2.java:35: yes is already defined in main(java.lang.String[])
int yes;
^
1 error

Tool completed with exit code 1

[marc weber]

christian loran wrote:...this was the error message!

C:\Users\christian\Desktop\document2.java:35: yes is already defined in main(java.lang.String[])
int yes;
^
...

This is telling you that the variable "yes" you tried to define on line 35 has already been defined within your main method. Indeed, you have a boolean "yes" defined on line 27 and an int "yes" defined on line 35. You can't declare 2 variables by the same name (in the same scope).

[fred rosenberger]

That should be easy for you to fix...don't define it twice. You have a boolean variable 'yes' on line 27, and an int yes variable defined on 35. You can't have two variables with the same name (well, technically you can, but for now let's pretend we can't).

although, I have to say that 'yes' and 'no' are not very good names for variables.

[christian loran]

thanks for the quick response, well now I am at a point were I do not know what to do... which variable yes should I remove? the one from the boolean or int?

here is the code:

/*  Protoype program to be used to prove  first concepts Algorithm project */

import java.io.*;

import java.lang.*;

import java.text.*;

import java.util.*;

//Set up public class

public class  document2

{

//declare main() method

public static void main(String[] args) throws IOException

{

//Declare data types

float length,width,area,circum;

boolean yes,no;

//set up input stream

Scanner  readin = new Scanner(System.in);

//prompt for length

int yes;
do
{

System.out.println("\n\n enter value for length");

//stream in length and convert to float

length = readin.nextFloat();

//prompt for width

System.out.println("\n\n enter value for width");

//stream in width and convert to float

width = readin.nextFloat();

//Calculate results

area = length*width;

circum = 2* (length + width);

//prepare data for out put display

 DecimalFormat twodig = new DecimalFormat("########.##");

 System.out.print("\n\nThe results of the calcuations are\n\n\n");

 System.out.print("the area is:\t\t"  +  twodig.format(area) + "\n\n");

 System.out.println("the circumference is:\t\t" + twodig.format(circum));

 //prompt for loop

 System.out.println("\n\n calculate again YES / NO ?");

 //stream in width and convert to float

 } while (no);





 }//end main

 }//end class

compile message:
C:\Users\christian\Desktop\document2.java:35: yes is already defined in main(java.lang.String[])
int yes;
^
1 error

Tool completed with exit code 1

[christian loran]

if yes and no are bad names for the variables, what names should I choose? Thank you!

[fred rosenberger]

christian loran wrote:if yes and no are bad names for the variables, what names should I choose? Thank you!

well...what do they represent? Generally, you name a variable so that when you come across it in your code, you'd know what it was. so "loopAgain" might be a good name for the variable that holds whether you want to loop through your code another time.

I don't see where you actually ever USE them, so why not just get rid of them?

[christian loran]

here are the new changes I made, still no luck. what changes should I make so that the program will run correctly. I want the user to be able to type yes or no to tell the program to loop or end. So should I add a value to yes and no? or just go with what you said before, int loopagain.

/*  Protoype program to be used to prove  first concepts Algorithm project */

import java.io.*;

import java.lang.*;

import java.text.*;

import java.util.*;

//Set up public class

public class  document2

{

//declare main() method

public static void main(String[] args) throws IOException

{

//Declare data types

float length,width,area,circum;

boolean no;

//set up input stream

Scanner  readin = new Scanner(System.in);

//prompt for length
int loopagain;
do
{

System.out.println("\n\n enter value for length");

//stream in length and convert to float

length = readin.nextFloat();

//prompt for width

System.out.println("\n\n enter value for width");

//stream in width and convert to float

width = readin.nextFloat();

//Calculate results

area = length*width;

circum = 2* (length + width);

//prepare data for out put display

 DecimalFormat twodig = new DecimalFormat("########.##");

 System.out.print("\n\nThe results of the calcuations are\n\n\n");

 System.out.print("the area is:\t\t"  +  twodig.format(area) + "\n\n");

 System.out.println("the circumference is:\t\t" + twodig.format(circum));

 //prompt for loop

 System.out.println("\n\n calculate again YES / NO ?");

 //stream in width and convert to float

 } while (no);





 }//end main

 }//end class

this was the compile message:

C:\Users\christian\Desktop\document2.java:74: variable no might not have been initialized
} while (no);
^
1 error

Tool completed with exit code 1

[christian loran]

If anyone can modify my code to make it properly loop that would be a huge help! Its hard trying to learn from a book, and I dont have an example of a working loop for my situation. feel free to add in any code to make it work, and the names of values do not matter, as long as it loops when the user types yes and ends when they type no. I realise the program is fairly simple though I am completely new to java and I am used to learning visusally and having a professor that includes samples. Thank you so much for all the help!

here is the code!

/*  Protoype program to be used to prove  first concepts Algorithm project */

import java.io.*;

import java.lang.*;

import java.text.*;

import java.util.*;

//Set up public class

public class  document2

{

//declare main() method

public static void main(String[] args) throws IOException

{

//Declare data types

float length,width,area,circum;

boolean no;

//set up input stream

Scanner  readin = new Scanner(System.in);

//prompt for length
int loopagain;
do
{

System.out.println("\n\n enter value for length");

//stream in length and convert to float

length = readin.nextFloat();

//prompt for width

System.out.println("\n\n enter value for width");

//stream in width and convert to float

width = readin.nextFloat();

//Calculate results

area = length*width;

circum = 2* (length + width);

//prepare data for out put display

 DecimalFormat twodig = new DecimalFormat("########.##");

 System.out.print("\n\nThe results of the calcuations are\n\n\n");

 System.out.print("the area is:\t\t"  +  twodig.format(area) + "\n\n");

 System.out.println("the circumference is:\t\t" + twodig.format(circum));

 //prompt for loop

 System.out.println("\n\n calculate again YES / NO ?");

 //stream in width and convert to float

 } while (no);





 }//end main

 }//end class

here is the compile message

C:\Users\christian\Desktop\document2.java:74: variable no might not have been initialized
} while (no);
^
1 error

Tool completed with exit code 1

[fred rosenberger]

christian loran wrote:If anyone can modify my code to make it properly loop that would be a huge help!

We don't do that here. This is your homework, so you need to do the work. If someone where to post the solution here, I would delete it.

You know how to get input from a user - you've done that. You need to do it again. On line 70, you ASK the user if they want to go again, but you haven't gotten an answer from them.

How did you get the input from the user for the length? You have to get their answer and store it somewhere. Once you have it, then you need to see if what they gave you requires you to loop again.

As to your current error, the compiler tells you exactly what the problem is. You have a (still poorly named) variable called "no" that has never been initialized. Local variable - variables declared inside a method - MUST be given a default, initial value. Your "no" variable is a boolean, so you need to set it initially to either 'true' or 'false' when you declare it back on line 27.

[christian loran]

I completely understand, I just made some more changes and got it to work, though I am having problems with the loop, how should I go about getting the users answers yes and no to have effects on weather the program loops?

/*  Protoype program to be used to prove  first concepts Algorithm project */

import java.io.*;

import java.lang.*;

import java.text.*;

import java.util.*;

//Set up public class

public class  document2

{

//declare main() method

public static void main(String[] args) throws IOException

{

//Declare data types

float length,width,area,circum,decision;

boolean endprogram;

endprogram = true;

//set up input stream

Scanner  readin = new Scanner(System.in);

//prompt for length
int loop;
do
{

System.out.println("\n\n enter value for length");

//stream in length and convert to float

length = readin.nextFloat();

//prompt for width

System.out.println("\n\n enter value for width");

//stream in width and convert to float

width = readin.nextFloat();

//Calculate results

area = length*width;

circum = 2* (length + width);

//prepare data for out put display

 DecimalFormat twodig = new DecimalFormat("########.##");

 System.out.print("\n\nThe results of the calcuations are\n\n\n");

 System.out.print("the area is:\t\t"  +  twodig.format(area) + "\n\n");

 System.out.println("the circumference is:\t\t" + twodig.format(circum));

 //prompt for decision

 System.out.println("\n\n calculate again yes / no ?");

 //stream in loop and convert to float

decision = readin.nextFloat();



 //stream in width and convert to float

 } while (endprogram);




 }//end main

 }//end class

[Mykhailo Kozik]

I recommend you to read basics, it will be really helpful.

So, you can try this pattern for interactive loop:

Scanner scanner = new Scanner(System.in);
		boolean isExit = false;
		while (!isExit){
			System.out.println("Do you wanna exit? yes/no");
			String decision = scanner.nextLine();
			isExit = decision.equals("yes");
		}