将十进制int转换为二进制

Question

The task i have is to write a method which converts any decimal number to binary, the number is given as an int and the converted (binary) number should also be returned as an int. Now i got somewhat of a solution, but i dont know how to save the converted number as an int, as I'm working with a string in my method! I feel like .parseInt() would be too easy, because then I could also just use . toBinaryString() . toBinaryString()

static void intToBin (int a) {

String bin = "";

while (a > 0) {
    if ( a % 2 == 0 )
        bin = bin + "0";
    else
        bin = bin + "1";
    a /= 2;
}

for (int i = 0; i < bin.length();i ++) {
    System.out.print(bin.charAt(i));
}

Answer 1

First, binary representation is just that, the value of a decimal number into a binary string. Or decimal is just a representation of a binary number. If you convert a binary number to an int it will be a decimal number (whether it has only 1's and 0's or not).

int a = 1001;  //is a decimal number  == 1,001
int b = 0b1001; //is a decimal number == 9

The above would print in decimal because that is the default output representation of the print methods. Internally, all numbers are 1's and 0's (or possibly even +5v and 0v depending on how specific you want to be).

If you want to convert a binary string to decimal, do it similarly. Except instead of dividing by the two and getting the remainder, you multiply by two.

int sum =0
String s = "11011";  //27
for (char c : s.toCharArray()) {
   sum = sum * 2 + (c-'0'); // multiply by 2 and add the bit.
}
System.out.println(sum);

prints

27

Note that I don't need to store it as a string since decimal is the default representation (as I explained earlier).

Answer 2

This would do what you're asking for:

public static int decimalToBinary(int a) {
    String result = "";
    while (a > 0) {
        int res = a % 2;
        a = a / 2;
        result = res + result;
    }
    return Integer.parseInt(result);
}

Answer 3

String text = etxtDecimal.getText().toString();
binary = Integer.toBinaryString(Integer.parseInt(text));

It is. We use toBinaryString to convert decimal to binary

Answer 4

Just a note, instead of needing the loop:

for (int i = 0; i < bin.length();i ++) {
    System.out.print(bin.charAt(i));
}

the digits could be added in front to the result:

...
if ( a % 2 == 0 )
    bin = "0" + bin;
else
    bin = "1" + bin;
...
System.out.println(bin);

(could also just add the result of a % 2 , without the need of the if _{not sure if better} )

---

if you want to save the binary representation as an int (bit strange, confusing).
Example: input 5 , output 101

int bin = 0;
int mult = 1;
while (a > 0) {
    if (a % 2 == 1) {
        bin += mult;
    }
    mult *= 10;
    a /= 2;
}

^{not tested, just an idea, to inspire}