c++ - Decimal to binary without arrays and binary-operators (like "&")

Question

I have to do a task for the university to write a program that converts a decimal number into binary. As I am only in a preliminary course of computer science, there were no arrays or bitwise operators (like '&') introduced yet. The program needs to be written using basic operators (+,-,*,%) and (if-else,for) only. My approach is the following, but I always get the inverted value. So instead of 1100, 0011.

#include <iostream>
int main()
{
   int n,a;
   std::cin >> n;
   
   for (int i=n; n>0; --i) {
       
     a = n%2;
     std::cout << a;
     n = n/2;
   
   }

   return 0;
}

is there a way to solve this problem?

Answer 1

Your current code checks for presence of the binary value from LSB to MSB, and prints in that order. One way to approach the issue would be to instead check from MSB to LSB.

#include <iostream>
int main(){
  int n, a=1;
  std::cin >> n;

  while(2*a <= n)
    a *= 2;                                                                                                               
  while(a > 0){
    if (n >= a){
      std::cout << 1;
      n -= a;
    } else {
      std::cout << 0;
    }
    a /= 2;
  }
  std::cout << std::endl;
  return 0;
}

This isn't a great way to do this, and I recommend improving it or finding alternatives as an exercise.