Thread: Beginner needs help with simple java assignment.

I'm trying to implement a program that reads binary numbers from the user and returns the equivalent in the normal (decimal) numeral system.

This is what I've come up with so far:

 import java.util.Scanner;
public class BinaryConverter {
 
		public static void main(String[] args) {
		int binary;
		Scanner scan = new Scanner (System.in);
		System.out.print("Enter a binary number (0 to quit): ");
		binary = scan.nextInt();	
		String binaryString = Integer.toString(binary);
		while (binary != 0)
			System.out.println("The binary number " +binaryString +" corresponds to " +toDecimal(binaryString)+" in the decimal numeral system.");
 
 
}
 
public static double toDecimal(String binaryString)
{
	double decValue = 0;
	int i = 0;
	for(i=0; i < binaryString.length(); i++)
		if (binaryString.charAt(binaryString.length() - i) == 1){
			decValue = Math.pow(2, binaryString.length()- i );
		}
return decValue;
 
}

My program fails to carry out this task.
What can I do to ensure that the variable decValue summarizes the result from "decValue = Math.pow(2, binaryString.length()- i " each and every time the for-loop is runned through and invokes that code?

I also get a string index out of bound error, but I can't see where the program errs.

Any help is appreciated.

You reset the decValue every time though the loop, rather than incrementing it:

decValue [COLOR="Red"]+=[/COLOR] Math.pow(2, binaryString.length()- i );

Also, inspect your loops closely. You are getting exceptions because your loop is written in such a way as to try and access an array element that is not within its bounds.

Ok, I've made som necessary changes to the program.

Code:

 import java.util.Scanner;
public class BinaryConverter {
 
		public static void main(String[] args) {
		int binary = 2;
		Scanner scan = new Scanner (System.in);
		String binaryString = Integer.toString(binary);
		while (binary != 0){
			System.out.print("Enter a binary number (0 to quit): ");
			binary = scan.nextInt();
			System.out.println("The binary number " +binary +" corresponds to: " +toDecimal(binaryString));
		}
 
}
 
		public static double toDecimal(String binaryString) {
		    double decValue = 0;
		    for (int i=0; i < binaryString.length(); i++)
		        if (binaryString.charAt(i) == '1')
		            decValue += Math.pow(2, binaryString.length() - 1 - i);
		    return decValue;
		}  
 
 
}

I have two problems, firstly, the program will just return 0.0 from any input. Secondly, the program doesn't quit when the user enters zero. The latter is a minor problem, but advice on both problems are highly appreciated.