Compiles fine but get error when I try to execute

[kowbonez]

When I try to run the program, it comes up with this error window:
http://i.imgur.com/M1ClO.jpg

#include <iostream>
#include <string>
#include <sstream>
#include<fstream>
using namespace std;

string BlankSpace(const string & a);
string NumWords(string user_input);


int main()
{
 
	char UserInput[256];
	fstream Lines;
	Lines.open( "lines.txt");
	
	cout << "Enter your string " << endl;
    while( Lines.getline(UserInput, 256) )
		cout <<  BlankSpace(UserInput) << endl;
	
	
	string userinput= BlankSpace(UserInput);
	string numwords= NumWords(userinput);

	cout << "There are " << numwords << "words in your string." << endl;
	cout << endl;

	

    cin.get();
    return 0;
}



string BlankSpace(const string & a)
{
	istringstream iss(a);
    string result;
    string input;
	 
    while (iss>>input)
    {
        result+=input;
        result+=' ';
    }

	
    result.erase(result.end()-1);

    return result;
	
}

string NumWords(string user_input)
{
	int numspaces;
	char nextChar;
	string NumSpaces;

	numspaces= 0;
	for (int i=0; i< int(user_input.length()); i++)
	{
		nextChar = user_input.at(i);
		if (isspace(user_input[i]))
			numspaces++;
	}
	NumSpaces= numspaces;

	return NumSpaces;
}

[Moschops]

Your code throws an exception of type length_error; http://www.cplusplus.com/reference/std/stdexcept/length_error/

Have a look at this line; result.erase(result.end()-1);

If it looks fine to you, no worries; stick some debugging code just ahead of it so you can get some information on every result you pass into it. Take a look at the usual sorts of things; what characters are actually in the string, how big the string is, that sort of thing.