[STL] example of the standard library count_if

/*|| Using a more complex function object*/#include <iostream.h>#include <string>#include <list>#include <algorithm>//predicate function objectclass IsAToothbrush {public:  IsAToothbrush(string& InToothbrushCode) :       ToothbrushCode(InToothbrushCode) {}  bool operator() (string& SalesRecord)   {    return SalesRecord.substr(0,4)==ToothbrushCode;  }       private:  string ToothbrushCode;        };int main (void) {  list<string> SalesRecords;  SalesRecords.push_back("0001 Soap");  SalesRecords.push_back("0002 Shampoo");  SalesRecords.push_back("0003 Toothbrush");  SalesRecords.push_back("0004 Toothpaste");  SalesRecords.push_back("0003 Toothbrush");    string VariableToothbrushCode("0003");  int NumberOfToothbrushes(0);/*  count_if (SalesRecords.begin(), SalesRecords.end(),               IsAToothbrush(VariableToothbrushCode),                 NumberOfToothbrushes);*/  NumberOfToothbrushes = count_if (SalesRecords.begin(), SalesRecords.end(),               IsAToothbrush(VariableToothbrushCode));  cout << "There were  "       << NumberOfToothbrushes        << " toothbrushes matching code "       << VariableToothbrushCode       << " sold"        << endl;}