Question

How would I go about debugging this to make it work properly?

import java.util.Scanner;

public class TemperatureConverter{
        
 public static void main(String[] args) {
        
         // Declare named constants.
         
         final double MIN_FAHRENHEIT = -459.67;
         
         // Declare the variables. 
 
         double fahrenheit;
         double convertedDegrees;
         int tempScale;
         String tempScaleStr="";
 
         // Creating the Scanner object
         Scanner keyboard =  new Scanner(System.in);
 
         System.out.print("Enter the temperature in Fahrenheit: ");               
         fahrenheit =  keyboard.nextDouble();  // Set a breakpoint here   
 
         // Verify the user's input
         if (fahrenheit > MIN_FAHRENHEIT) {   // first if-statement: Set a breakpoint here
                 System.out.print("The temperature must be greater than or equal to " + MIN_FAHRENHEIT);
                 System.exit(0);
         }
 
         System.out.print (
                         "Enter the temperature scales you want to convert to:\n"+ 
                         "1. Kelvin \n"+
                         "2. Rankine \n"+
                         "3. Reaumur \n"+
                         "4. Celsius\n"+
                         "Enter a temperature scale: ");
         tempScale = keyboard.nextInt();
         
         if (tempScale > 1 && tempScale < 4) {  // Second-if statement: Set a breakpoint here
                 System.out.println("Unknown temperature scale  -" +
                                                        "  cannot do calculation. Bye");
         }
         else {
                 if (tempScale == 1) { // Set a breakpoint here
                         convertedDegrees = fahrenheit + MIN_FAHRENHEIT*5/9;
                         tempScaleStr="Kelvin"; 
                 } else if (tempScale == 2 || tempScale == 3) { 
                        convertedDegrees = convertedDegrees - MIN_FAHRENHEIT;  
                        tempScaleStr="Rankine";
                        
                 } else if (tempScale == 3) { 
                         convertedDegrees = fahrenheit - 32*4/9 ; // Set a breakpoint here
                         tempScaleStr="Rankine";
                                 
                 } else {
                         convertedDegrees = (fahrenheit - 32)*9/5; // Set a breakpoint here
                         tempScaleStr="Celsius";
                 }

                 System.out.println(fahrenheit + " degrees Fahrenheit is " + convertedDegrees + " degrees "+ tempScaleStr + ".");
         }
 }
}

Answer 1

Note: You have commited mistakes in only 2 areas, one is verify the user input area where first if-statement is used and next is second if-statement is used. There we have to reverse the conditional operators so that the functionality is worked. Following is the debugged code.

Debugged code for above problem

import java.util.Scanner;

public class TemperatureConverter{
   public static void main(String[] args) {
      
         // Declare named constants.
       
         final double MIN_FAHRENHEIT = -459.67;
       
         // Declare the variables.

         double fahrenheit = 0.0;
         double convertedDegrees = 0.0;
         int tempScale = 0;
         String tempScaleStr="";

         // Creating the Scanner object
         Scanner keyboard = new Scanner(System.in);

         System.out.print("Enter the temperature in Fahrenheit: ");             
         fahrenheit = keyboard.nextDouble(); // Set a breakpoint here

         // Verify the user's input
         if (fahrenheit < MIN_FAHRENHEIT) {   // first if-statement: Set a breakpoint here
                 System.out.print("The temperature must be greater than or equal to " + MIN_FAHRENHEIT);
                 System.exit(0);
         }

         System.out.print (
                         "Enter the temperature scales you want to convert to:\n"+
                         "1. Kelvin \n"+
                         "2. Rankine \n"+
                         "3. Reaumur \n"+
                         "4. Celsius\n"+
                         "Enter a temperature scale: ");
         tempScale = keyboard.nextInt();
       
         if (tempScale < 1 && tempScale > 4) { // Second-if statement: Set a breakpoint here
                 System.out.println("Unknown temperature scale -" +
                                                        " cannot do calculation. Bye");
         }
         else {
                 if (tempScale == 1) { // Set a breakpoint here
                         convertedDegrees = fahrenheit + MIN_FAHRENHEIT*5/9;
                         tempScaleStr="Kelvin";
                 } else if (tempScale == 2 || tempScale == 3) {
                        convertedDegrees = convertedDegrees - MIN_FAHRENHEIT;
                        tempScaleStr="Rankine";
                      
                 } else if (tempScale == 3) {
                         convertedDegrees = fahrenheit - 32*4/9 ; // Set a breakpoint here
                         tempScaleStr="Rankine";
                               
                 } else {
                         convertedDegrees = (fahrenheit - 32)*9/5; // Set a breakpoint here
                         tempScaleStr="Celsius";
                 }

                 System.out.println(fahrenheit + " degrees Fahrenheit is " + convertedDegrees + " degrees "+ tempScaleStr + ".");
         }
}
}

Sample output

Mention in comments if any mistakes or errors are found. Thank you.