Why is my code only printing last line to txt file.

#include<iostream> //i.o
#include<cctype> //for isdigit
#include<sstream> //to phrase string
#include<string>
#include <vector>
#include <fstream>
#include <sstream>
#include <algorithm>
#include<bits/stdc++.h>
#include<iostream> //i.o
#include<cctype> //for isdigit
#include<sstream> //to phrase string
#include<string>
#include <vector>
#include <fstream>
#include <sstream>
#include <algorithm>
using namespace std;

void splitString(string str)
{ofstream out("example.txt");
    string alpha, num, special;
    for (int i=0; i<str.length(); i++)
    {

         if((str[i] >= 'A' && str[i] <= 'Z') ||
                (str[i] >= 'a' && str[i] <= 'z'))
           break;

           else if (isdigit(str[i]))
            num.push_back(str[i]);
    }


    out << num<<endl;

}

// Driver code
int main()
{

std::string word;
    std::vector<std::string> file;

    std::ifstream in( "Files.txt" );

    while ( in >> word )
        file.push_back( word );

    for ( size_t i=0; i<file.size(); i++ ){




    string str = file.at(i);
    splitString(str);}
    return 0;
}