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Thread: Problem with looping

  1. #1
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    Default Problem with looping

    I'm a beginner in Java and I wanted to create a program where I can convert from celsius to fahrenheit but I need to be able to read and process data from a text file also. The text file has 5 lines of text each with different numeric values and when I run my program I'm only able to do a conversion for the first line of text. I know that I should be able to get my program to read all of the lines and do the calculations with a loop but I'm not sure how to do it. Any suggestions would be helpful. Here is my code so far:

    import java.util.Scanner;
    import java.io.*;
     
    public class CToFConversion {
     
    		char symbol = '\u00B0'; // this is the unicode "degree" symbol
    		Scanner myScanner= new Scanner("tempdata.txt");
     
    		public void readFile(String file_name) {
    		try{
    			 File file = new File(file_name);
    			 Scanner myScanner= new Scanner(file);
    			 double celsius = myScanner.nextDouble();
    			 double Fahrenheit = 9.0 / 5 * (celsius + 32);
    			 System.out.print(celsius + " Celsius is" + " Fahrenheit ");
    			 System.out.printf("%5.1f", Fahrenheit);	
     
    		while(myScanner.hasNextLine()){
    			 System.out.println(myScanner.nextLine());	
    			}
     
    		}catch(Exception ex){
    			 System.out.println(ex.getMessage());
    			 System.exit(0);
    		}
     
    	}
    }

    I also used another class to run this program, this is the code for that:

    import java.io.*;
     
    public class CToFConversionLoop {
     
    	public static void main(String[] args) throws IOException {
     
    		CToFConversion conversion = new CToFConversion();
    		conversion.readFile("tempdata.txt");String file_name = "tempdata.txt";	
     
    	}
    }

    The text file has 5 lines:
    0.0
    33.3
    100.0
    -10.0
    -273.0


  2. #2
    Super Moderator Norm's Avatar
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    Default Re: Problem with looping

    What does your program print out when it executes?

    The program doesn't save the String that is returned by the nextLine() method. It should save the String that was read by assigning it to a String variable that can then be processed by the program.
    If you don't understand my answer, don't ignore it, ask a question.

  3. #3
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    Default Re: Problem with looping

    This is the result when it executes:

    0.0 Celsius is Fahrenheit 57.6
    33.3
    100.0
    -10.0
    -273.0

  4. #4
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    Default Re: Problem with looping

    There is code that reads the values from the file and computes a value.
    Can you put that code inside the loop?
    If you don't understand my answer, don't ignore it, ask a question.

  5. #5
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    Default Re: Problem with looping

    I've put the values used to do the calculations in the loop but for the first line of the text file it skips it. Is there a different method I should use instead of nextLine? This is the code:

    import java.util.Scanner;
    import java.io.*;
     
    public class CToFConversion {
     
    		char symbol = '\u00B0'; // this is the unicode "degree" symbol
    		Scanner myScanner= new Scanner("tempdata.txt");
     
    		public void readFile(String file_name) {
    		try{
    			 File file = new File(file_name);
    			 Scanner myScanner= new Scanner(file);	
     
    		while(myScanner.hasNextLine()){
    			 System.out.println(myScanner.nextLine());
    			 double celsius = myScanner.nextDouble();
    			 double Fahrenheit = 9.0 / 5 * (celsius + 32);
    			 System.out.print(celsius + " Celsius is" + " Fahrenheit ");
    			 System.out.printf("%5.1f", Fahrenheit);	
    			}
     
    		}catch(Exception ex){
    			 System.out.println(ex.getMessage());
    			 System.exit(0);
    		}
     
    	}
    }

    This is my output:
    0.0
    33.3 Celsius is Fahrenheit 117.5
    100.0 Celsius is Fahrenheit 237.6
    -10.0 Celsius is Fahrenheit 39.6
    -273.0 Celsius is Fahrenheit -433.8

  6. #6
    Super Moderator Norm's Avatar
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    Default Re: Problem with looping

    First line of the text file it skips it.
    The String read by the nextLine() method is printed and then is thrown away and not saved. What is the purpose of the statement:
     System.out.println(myScanner.nextLine());
    The data on every line read by nextLIne() in this statement is lost to the program.


    This statement reads a value from the file, converts it to double and saves its value in a variable that is used in later computations:
    double celsius = myScanner.nextDouble();
    If you don't understand my answer, don't ignore it, ask a question.

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