Program on C++ that trasform int to string, string to int, char to int

Hi, today it's gonna be another C++ program that finds all numbers between 1000 and 10 000 (it's four - digitnumbers and this interval can be changed).
Those numbers looks like abcd where a,b,c,d - all different  and ab - cd = a+ b+c+d .

So to write it I choosed the way to change the numbers in strings. So now it really easy to check if conditions are met.

To transform int to string on C++ I used itoa function and to transform string to int on C++ I used atoi function.

To transform char to int on C++ I used code like this:

char s;

cin>>s;

int i = s - '0';

 So here is the code:


#include "stdafx.h" 
#include <iostream> 
#include <string> 
#include <stdio.h> 
#include <stdlib.h> 


using namespace std; 
// itoa : int to string; 
// atoi : string to int; 


int _tmain(int argc, _TCHAR* argv[]) 
{ 
  string abs;   
  string cds;     
  int sum = 0;
  int n; 


  for(int n = 1000; n < 10000; n++)
  {
     char buffer[5];
     string str = itoa(n, buffer, 10); 
     int k = 1;


     for(int i = 1; i< 4; i++) 
      if (str[i-1] != str[i]) 
        k++;   
    if (k == 4)   
    { 
      abs = str[0]; 
      abs += str[1];
      cds = str[2]; 
      cds += str[3]; 


       sum += (str[0]-'0') + (str[1]-'0') + (str[2]-'0') + (str[3]-'0'); 


      int iab = atoi(abs.c_str());
      int icd = atoi(cds.c_str()); 
      if (iab - icd == sum)  
       cout<<n<<endl; 


      sum = 0;
     };


   } 


   return 0;


 }