dec2bin.cpp

#include <iostream>
#include <cstdlib>
#include <algorithm>
#define LEN 256

char* dec2bin(int dec);

int main(int argc, char *argv[]) {
  if(argc != 2) {
    std::cout << "Input is required" << std::endl;
    return 1;
  }

  std::cout << "Result: 0b";

  /*
    A smarter way would be fill the array starting by its end, and then using a compact-like method to delete all the
    dirty trash in the string, but I've chosen the faster way.
    Another good way (shorter but slowest with big numbers because of the overhead) would be using a recursive algorithm.
  */
  int i;
  char *bin;
  for(i = LEN, bin = dec2bin(std::atoi(argv[1])); i >= 0; --i)
    if(bin[i] == '0' || bin[i] == '1')
      std::cout << bin[i];

  std::free(bin);
  std::cout << std::endl;
  return 0;
}

char* dec2bin(int dec) {
  int i     = 0;
  char *bin = new char[LEN]();

  while(dec > 0) {
    bin[i++] = dec % 2 == 0 ? '0' : '1';
    dec /= 2;
  }

  bin = (char*)std::realloc(bin, i * sizeof(char));

  return bin;
}