java二进制转十进制转换器

Question

This is one of my first Java programs and I am very confused why it doesn't work. Help?

In addition, the else statement prints despite 'input' being given a correct value. Is there a structure for conditional statements that I'm missing?

package beginning;
import java.util.Scanner;
import java.lang.Math;

// VERY BROKEN

public class BinaryDecimalConverter {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Scanner sc = new Scanner(System.in);
        System.out.println("Number Base To Convert: 1) Binary 2) Decimal ::");
        String binOrDec = sc.next();
        System.out.println("Enter Number ::");
        long number = sc.nextInt();
        double result = 0;

        if ((binOrDec.equals("1")) || (binOrDec.equals("Binary"))) {
            char[] bin = ("" + number).toCharArray(); // conversion must be String >> char[]
            int index = bin.length - 1;
            double aggregate = 0;
            for (int i = 0; i < bin.length; i++) {
                aggregate = ((Math.pow(2, i)) * (bin[index])); // when using Math.pow(a, b) - a must be 'double' data type
                index = index - 1;
                result = result + aggregate;
            }   
        }
        if (binOrDec.equals("2") || binOrDec.equals("Decimal")) {
            // decimal-binary converter, unfinished.
        }
        else {
            System.out.println("Invalid Input");
        }

        System.out.println("" + number + " >> " + result);
        sc.close();

    }

}

Answer 1

your code says: if binOrDec is 2 or Decimal , do nothing, else, print invalid input . Computers do what you tell em to. I think you probably want an else in front of that line to checks for 2/Decimal.

'doesn't work' is not a great start. Help us help you:

• If it does not compile, tell us the error the compiler gives you and make sure the line numbers match up or you otherwise make it possible for us to know where to look.
• If it does compile, but you get an error when you run it, supply the error, as well as any input you provided that resulted in the error.
• If it does compile, and run, and you get output, but it is not the output you expected, explain what you typed in to get it, what you did expect, and why.

Your bin array is of type char[] . If I supply the binary number 1010 for example, it contains 4 characters: 1, 0, 1, and 0. That's characters . ascii characters. The ascii character 1 has a large numeric value (not 1 ):

char c = '1';
System.out.println(1 * c);

The above prints.... 49 .

So: aggregate = ((Math.pow(2, i)) * (bin[index])); is multiplying by 48 or 49 depending on whether that character is a 1 or a 0. I think you may be looking for if (bin[index] == '1') aggregate = Math.pow(2, i); .