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Thread: Reading from a txt file and loop trouble

  1. #1
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    Default Reading from a txt file and loop trouble

    The code:

    // This program will read in from a file a series of numbers in degrees
    // Celsius, convert them to degree Fahrenheit and print out a table of 
    // those values.  The file input is handled using the command line's 
    // redirection mechanism.
     
    import java.util.Scanner;
     
    public class Lab4b
    {
       public static void main(String[] args)
       {
          // Declare variables
          Scanner scan = new Scanner(System.in);
     
          double degreeCelsius;
          double degreeFahrenheit;
     
          // Print to the screen the header of the output table
          // as seen in the sample run below.
          // There are two lines in the header.
          // Make sure it has the right spacing to line up with the table.
          System.out.println("Celsius    | Fahrenheit");
          System.out.println("-----------+-----------");
     
          // Write your loop here
          // We want to loop until there are no more inputs to be read. 
     
          while( scan.hasNext())
          {
             // Check to see if the input is a double.
             // If a double read in and store in degreeCelsius.
             // If not a double print an error message and quit.
             if (scan.hasNextDouble())
    			degreeCelsius = scan.nextDouble();
     
    		 else
    		 {
    			System.out.println("Error in input");
    			System.out.println("Programming is terminating...");
    		        System.exit(0);
    		 }
     
     
             // Convert input degrees Celsius to degrees Fahrenheit
             // and store in degreeFahrenheit.
             // f = c * (9.0/5.0) + 32.0
     
             degreeFahrenheit = degreeCelsius * (9.0/5.0) + 32.0;
     
             // Display to the screen the output as shown in the 
             // sample run below.  Use System.out.printf.  Make sure
             // that everything lines up properly.
             System.out.printf("       degreeCelsius%d|       degreeFahrenheit%d%n");
     
          } // End of loop
       } // End of main method
    } // End class

    I cant figure out what I am doing wrong in the loop.

    When I try and compile I get an initialization error

    C:\Users\Mitchell\My Documents\cs1113\Labs>javac Lab4b.java
    Lab4b.java:52: error: variable degreeCelsius might not have been initialized
    degreeFahrenheit = degreeCelsius * (9.0/5.0) + 32.0;

    So.. I set degreeCelsius = 0;
    Then it compiles but when I run the command java Lab4b < lab4data.txt


    C:\Users\Mitchell\My Documents\cs1113\Labs>java Lab4b < lab4data.txt
    Celsius | Fahrenheit
    -----------+-----------
    degreeCelsiusException in thread "main" java.util.MissingFormatArgumentEx
    ception: Format specifier 'd'
    at java.util.Formatter.format(Formatter.java:2487)
    at java.io.PrintStream.format(PrintStream.java:970)
    at java.io.PrintStream.printf(PrintStream.java:871)
    at Lab4b.main(Lab4b.java:57)

    So either I am having trouble with the loop or the printf statement
    Any hints/tips on those would be great



    Here is the txt file it has to read in:
    5.5
    15.2
    25.4
    35.8
    45.1
    55.9
    65.3
    75.7
    85.6
    95.0

    And here is the print format is has to look like:

    command in cmd: java Lab4b < lab4data.txt

    Celsius | Fahrenheit
    -----------+-----------
    5.50| 41.90
    15.20| 59.36
    25.40| 77.72
    35.80| 96.44
    45.10| 113.18
    55.90| 132.62
    65.30| 149.54
    75.70| 168.26
    85.60| 186.08
    95.00| 203.00

    ^^^^The lines have to match up^^^^
    Last edited by LaMigra; September 18th, 2014 at 05:19 AM.


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    Default Re: Reading from a txt file and loop trouble

    Welcome to the forum. Good first post . . . except, please describe what you need help with. Ask a specific question or describe the problem. If you're getting compiler or runtime errors, please post the entire error message with the stack trace, as appropriate. If logic or output errors, show a sample run by copying your console and pasting it into a post.

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    Default Re: Reading from a txt file and loop trouble

    Quote Originally Posted by GregBrannon View Post
    Welcome to the forum. Good first post . . . except, please describe what you need help with. Ask a specific question or describe the problem. If you're getting compiler or runtime errors, please post the entire error message with the stack trace, as appropriate. If logic or output errors, show a sample run by copying your console and pasting it into a post.
    edited for clarification.

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    Default Re: Reading from a txt file and loop trouble

    Local variables must be initialized, as in:

    int localVariable = 0;

    printf() can be confusing. Your statement should look something like:

    System.out.printf(" %f| %f\n", degreeCelsius, degreeFahrenheit );

    but you'll need to adjust it to get the desired output format.

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    Default Re: Reading from a txt file and loop trouble

    Quote Originally Posted by GregBrannon View Post
    Local variables must be initialized, as in:

    int localVariable = 0;

    printf() can be confusing. Your statement should look something like:

    System.out.printf(" %f| %f\n", degreeCelsius, degreeFahrenheit );

    but you'll need to adjust it to get the desired output format.
    Thank you I kinda out the printf. Need the printf format to make the output a double.

    but I encountered this when I initialized degreeCelsius = 0;

    C:\Users\Mitchell\My Documents\cs1113\Labs>java Lab4b < lab4data.txt
    Celsius | Fahrenheit
    -----------+-----------
    0.000000| 32.000000
    0.000000| 32.000000
    0.000000| 32.000000
    0.000000| 32.000000
    0.000000| 32.000000
    0.000000| 32.000000
    0.000000| 32.000000
    0.000000| 32.000000
    0.000000| 32.000000
    0.000000| 32.000000

    What do I need to do in the loop so the txt table loops through the temperature formula?

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    Default Re: Reading from a txt file and loop trouble

    Where does the posted code read from a file?
    If you don't understand my answer, don't ignore it, ask a question.

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    Default Re: Reading from a txt file and loop trouble

    Quote Originally Posted by Norm View Post
    Where does the posted code read from a file?
    Ok I figured out my initialization problem. Everything works great just need help with the printf format how to lose all those zero's in my printout.

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    Default Re: Reading from a txt file and loop trouble

    Look at the API doc for the printf() method. It has a link to the Format String syntax in the Formatter class.
    If you don't understand my answer, don't ignore it, ask a question.

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