Project Euler problem

hi all,
I haven't touched c++ in a while. I'm just doing it in today to solve a problem in Project Euler. This is problem 42. Find a triangle word.

Code:

#include <cmath>
#include <iostream>
#include <fstream>
#include <vector>
#include <algorithm>
#include <iterator>
#include <cstring>
#include <iomanip>

class TriangleFinder
{
private:
  int   TriangleCount;
public:
  TriangleFinder():TriangleCount(0) {}
  void  operator() (std::string);
  int print_result() const { return TriangleCount;};
};
    
void TriangleFinder::operator() (std::string sInput)
{
  int                   value=0;
  std::string::iterator it = sInput.begin();
  double                root;
  
  for ( ; it < sInput.end() ; ++it)
    {
      value+= (*it) -64;
    }
  // find out whether root is an interger.
  root  = sqrt(double(value)*8+1);
  if ( fabs(floor(root)-root) < 1e-6)
    {
      TriangleCount++;
    }
  /*  std::cout <<std::setw(10) << sInput
            <<std::setw(10) << root
            <<std::setw(10) << fabs(floor(root)-root)
            <<std::setw(10) << TriangleCount << std::endl;
  */
}

int main()
{
  using namespace       std;
  string                sTmp;
  vector<string>        vStr;
  ifstream              inFile("words.txt");
  TriangleFinder        Finder;
  
  while (getline(inFile,sTmp,','))
    {
      sTmp.erase(sTmp.begin());
      sTmp.erase(sTmp.end()-1);
      vStr.push_back(sTmp);
    }
  //  copy(vStr.begin(),vStr.end(),ostream_iterator<string>(cout,"\n"));
  for_each(vStr.begin(),vStr.end(),Finder);
  cout << Finder.print_result() << endl;
}

The problem i ran into is that

Code:

cout << Finder.print_result() << endl;

keep returning 0. Could someone please tell me why the member variable TriangleCount get overwrites with 0?

Interesting. It's something to do with using the for_each. I'm not enough of a C++ guy to know what's wrong. If you use an explicit loop it works correctly:

Code:

  for (vector<string>::iterator it = vStr.begin(); it != vStr.end(); ++it)
      Finder(*it);

Note that this iterator loop of yours works but is not technically correct:

Code:

  for ( ; it < sInput.end() ; ++it)
      value+= (*it) -64;

The comparison should be it != sInput.end(). Using < works because of implementation details you are not supposed to be relying on.

And "interger" (in your comment) has an extra r.

Originally Posted by oogabooga

Interesting. It's something to do with using the for_each. I'm not enough of a C++ guy to know what's wrong. If you use an explicit loop it works correctly:

Code:

  for (vector<string>::iterator it = vStr.begin(); it != vStr.end(); ++it)
      Finder(*it);

Note that this iterator loop of yours works but is not technically correct:

Code:

  for ( ; it < sInput.end() ; ++it)
      value+= (*it) -64;

The comparison should be it != sInput.end(). Using < works because of implementation details you are not supposed to be relying on.

And "interger" (in your comment) has an extra r.

Right, thanks for pointing that out. I'll make the change to the code. It's been a while, little details like that just just escape my memory.

Here's a simplified test program demonstrating the same thing. Hopefully the experts can explain it to us.

Code:

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

class Sum {
private:
    int n;
public:
    Sum() : n(0) {}
    void operator() (int i) { n += i; cout << n << ' '; }
    void print() { cout << '<' << n << ">\n"; }
};

int main() {
  vector<int> v;
  for (int i = 1; i <= 5; i++) v.push_back(i);

  Sum s1;
  for (vector<int>::iterator it = v.begin(); it != v.end(); ++it) s1(*it);
  s1.print();

  Sum s2;
  for_each(v.begin(), v.end(), s2);
  s2.print();
}

Output:

Code:

1 3 6 10 15 <15>
1 3 6 10 15 <0>

Code:

template<class InputIterator, class Function>
  Function for_each(InputIterator first, InputIterator last, Function f)
  {
    for ( ; first!=last; ++first ) f(*first);
    return f;
  }

the return f could be the reason for so much fail on my part.

Yep, you figured it out. for_each makes a copy of Function, so if you don't accept the return value the copy disappears and you're left with the original object. So it should be:

Code:

Finder = for_each(vStr.begin(),vStr.end(),Finder);

Yeah, that's the solution. Thanks for your help, oogabooga.