when entering a negative number it does not come up with the correct answer all

Question

when entering a negative number it does not come up with the correct answer all the time. Any ides on how to fix this?

import java.util.*;
import java.lang.Math;
public class BinaryToDecimal {
public static void main (String [] args){
Scanner keyIn = new Scanner(System.in);
int response;
// menu options to choose how to run the program and continue running the
// program until user decides to quit.
do{
System.out.println("Enter 1 to convert decimal to binary");
System.out.println("Enter 2 to convert binary to decimal");
System.out.println("Enter 3 to quit");
System.out.print("Please enter your choice: ");
response = keyIn.nextInt();
//choosing 1 uses case 1 for decimal conversion and 2 for binary conversion
switch(response)
{case 1:
System.out.println("");
System.out.print("Enter a whole number between -128 and +127: ");
int decimal = keyIn.nextInt();
while(decimal < -128 || decimal > 127)
{
System.out.print("Enter a whole number between -128 and +127: ");
decimal = keyIn.nextInt();
}
System.out.println("");
System.out.print(decimal + " converted into a binary is: ");
decConvert(decimal);
System.out.println("");
break;
case 2:
System.out.println("");
System.out.println("Enter a 8-bit binary number:");
String a = keyIn.next();
System.out.println("");
System.out.println(a + " converted into a decimal is: ");
int i = binconvert(a);
System.out.println(i);
break;
default:
break;
}
System.out.println("");
}while(response!=3);
System.out.println("The program has ended");
}
//method to convert from decimal to binary
public static void decConvert(int num){
String out = "";
if(num >= 0)
{
while(num > 0){
out += num % 2;
num = num/2;
}
int length = out.length();
while(length < 8){
out += 0;
length++;
}
String temp = "";
int y = 7;
//Start from right of string moving to left
while(y > -1){
temp += out.charAt(y);
y--;
}
System.out.print(temp);
}
else
{
num *= -1;
while(num > 0){
out += num % 2;
num = num/2;
}
int length = out.length();
while(length < 7){
out += 0;
length++;
}
out += 1;
String temp = "";
int y = 7;
//Start from right of string moving to left
while(y > -1){
temp += out.charAt(y);
y--;
}
System.out.print(temp);
}
}
//method to convert from binary to decimal
private static int binconvert(String a)
{
double j = 0;
for(int i = 0; i<a.length(); i++)
{
if(a.charAt(i)== '1')
j=j+ Math.pow(2, a.length()-1-i);
}
if(j > 128)
j = 128 - j;
else if(j == 128)
j = -128;
return (int) j;
}
}

Explanation / Answer

please use a simpler code to avoid confusion.Your code is too messed up with less clarity.I hope this code makes it simple for you and helpes you to implement your operations.

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