Find and Replace string in c++

#include<iostream>
#include<conio.h>
#include<string>
using namespace std;
int main()
{
 string str="ali maqood is good prorammer";
 int position;

 position=str.find(" ");                        // find the blankspace from the string
 while(position!=string::npos)              // npos  means if no position find
 {
 str.replace(position,1,"," );                 //   repace string  with ","    
 position=str.find(" ",position+1);        // increment  in the position  
  str.replace(22,1,"g" );                       // again repace "g" on position 22 s
 }    
 cout << str;
getch();
}