#include <iostream>
#include <string>
 
 
int main() {
    std::string const toReplace    = "ing";
    std::string const replacement  = "ed";
    std::string const separators   = " ";
 
    std::string string = " Hello  hing and   ning and ting ying ";
 
    std::string::size_type first = 0, last = 0;
    while (true) {
       first = string.find_first_not_of(separators, last);
       if (first == std::string::npos) {
          break;
       }
 
       last = string.find_first_of(separators, first);
       if (last == std::string::npos) {
          break;
       }
 
       std::string::size_type wordLength = last - first;
       if (wordLength >= toReplace.length()) {
          std::string::size_type tailFirst = last - toReplace.length();
          if (string.compare(tailFirst, toReplace.length(), toReplace) == 0) {
             string.replace(tailFirst, toReplace.length(), replacement);
          }
       }
    }
 
    std::cout << string << std::endl;
}
 
 

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