将整数转换为二进制并打印数字之和

Question

The code below is supposed to take an integer, convert it to binary, and then print the sum of the digits:

Example:

Input = 15 

( 15 in Binary is "1111" and 1+1+1+1 = 4 )

Output = 4

This is the code I have so far. However, it is not working as expected. If you input 15 , it returns 0 instead of 4 as explained above:

  Scanner in = new Scanner(System.in);
  int X = in.nextInt();

  String binary = Integer.toBinaryString(X);   

  int amount = 0;  
  String input = Integer.toString(X);

  for(int b = 0; b < binary.length(); b++){
     if (binary.charAt(b) == 1){
      amount++;
     }
  }

  System.out.println(amount);

Answer 1

Characters are always single and written in single quotes.

1 is the character which is extracted from String and it should be written in single quotes.

Here is the correct code:

if (binary.charAt(b) == '1'){
  amount++;
}

Answer 2

Shorter approach:

Scanner in = new Scanner(System.in);
int X = in.nextInt();
String binary = Integer.toBinaryString(X);   
String input = Integer.toString(X)
System.out.println(StringUtils.countMatches(input, "1"));

Answer 3

Binary operations are enougth

    int p = 0b10000000000000000000000000010101;
    int t = 0;
    for(int i=0; i<32; i++) {
        t += p & 1;
        p = p >> 1;
    }
    System.out.println(t);