Binary to Decimal - java

Question

I want to write a program which receive a string value and print the decimal number.

In addition, if the string value is not 1 or 0, I need to print a message.

I wrote this code but it is always getting inside the if command.

I Would appreciate your support!

Thank you

import java.util.Random; public class Decimal { public static void main(String[] args) { String input = (args[0]); int sum = 0; for (int i = 0; i <= input.length(); i++) { if (!(input.charAt(i) == '0') || (input.charAt(i) == '1')) { System.out.println("wrong string"); break; } char a = input.charAt(i); if (a == '1') { sum |= 0x01; } sum <<= 1; sum >>= 1; System.out.println(sum); } } }

change !(input.charAt(i) == '0') || (input.charAt(i) == '1') to !(input.charAt(i) == '0') && (input.charAt(i) == '1') — TheQAGuy
– TheQAGuy, Commented Nov 6, 2015 at 15:12
And that would still be wrong with the parens placed like that. — SBI
– SBI, Commented Nov 6, 2015 at 15:13
Rather sth like (!(input.charAt(i) == '0' || input.charAt(i) == '1')) — clsbartek
– clsbartek, Commented Nov 6, 2015 at 15:14

Andreas · Accepted Answer · 2015-11-06 15:22:39Z

The ! (not) operator of the if statement only applies to the first part:

if ( ! (input.charAt(i) == '0') || (input.charAt(i) == '1') ) {

So that is the same as:

if ((input.charAt(i) != '0') || (input.charAt(i) == '1')) {

When you actually meant to do:

if (input.charAt(i) != '0' && input.charAt(i) != '1') {

It's a good thing though, because once that works, you're going to get an IndexOutOfBoundsException when i == input.length(). Change the loop to:

for (int i = 0; i < input.length(); i++) {

And for performance, move variable a up and use it in that first if statement. Rename to c or ch is more descriptive/common.

Doing both sum <<= 1 and sum >>= 1 leaves you where you started. Is that what you wanted? You should also do the left-shift before setting the right-most bit.

Applying all that, I believe you meant to do this:

String input = args[0]; int sum = 0; for (int i = 0; i < input.length(); i++) { char c = input.charAt(i); if (c != '0' && c != '1') { System.out.println("wrong string"); break; } sum <<= 1; if (c == '1') sum |= 1; } System.out.println(sum);

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