Power of 2 Vs Power of 10

10 == 2^3
100 == 2^7
1,000 == 2^10 (thousand)
100,000 == 2^20 (million) (百萬)
1,000,000,000 = 2^30 (billion) (十億)

How much memory to create a reasonable index/hash table?

(3,10),(6,100),(9,1000),(13,10000),(16,100000),(19,1e+06),(23,1e+07),(26,1e+08),(29,1e+09),(33,1e+10),(36,1e+11),(39,1e+12),(43,1e+13),(46,1e+14),(49,1e+15)

#include <iostream>
#include <map>
using namespace std;

const int ORDER = 50;
double power10[ORDER];

double power2[ORDER];

template <typename T>
void print(T ARRAY,int len)
{

  for (int i=0;i<len;++i){
    cout<<ARRAY[i];

    cout<<(i==len-1?"":",");
  }
  cout<<"\n";
}

void print(map<double,double> m)
{
  map<double,double>::const_iterator c_itr;

  for (c_itr = m.begin() ;c_itr != m.end(); ++c_itr){

    cout <<"("<<c_itr->first<<","<<c_itr->second<<"),";
  }
}
void initialize()
{

  power10[0] = 10;
  power2 [0] = 2;

  for (int i=1;i<ORDER;++i){
    power10[i] = 1;

    power2[i] = 1;
  }
  for (int i=1;i<ORDER;++i){

    power10[i] = power10[i-1]*10;
    power2[i] = power2[i-1]*2;
  }
}

map<double,double> build_map()
{
  map<double,double> power_map;

  for(int i=0,j=0; i<ORDER; ++i){

    if (power2[i]>power10[j]){
      power_map[i] = power10[j];
      ++j;
    }    
  }

  return power_map;
}

int main()
{
  initialize();

  print(power10,ORDER);
  cout<<"\n";
  print(power2,ORDER);

  map<double,double> result_map = build_map();
  print(result_map);
}