Subtracting two numbers without using '-' operator

Question

i tried with the following code , but i can\'t understand why it\'s giving me wrong answer. i am computing the 2\'s complement and adding with another no.

#inclu         


        

Answer 1

add method implementation is incorrect. do like this -> A java way of this.

public int add(int a, int b){
  do {
    a = a & b; //carry
    b = a ^ b;  //addition
    a = a << 1; //carry shift to one bit left
  }while(a != 0);  //exit 
  return b;     //addition result
}

  public int sub(int a, int b){
    return add(a, add(~b, 1)); 

  }