C++ :: Input Text From One File To Another

Code:
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main() {
ifstream wormfile("worm.txt");
ofstream dtfile("dt.txt");

[Code] ....

worm.txt has

Code:
I like pie
I like rice
and I like applesauce
while dt.txt has nothing

I was able to get the lines in worm.txt and get it to copy the lines to dt.txt BUT it looks like I can do this in some kind of if statement or while loop. The reason why I don't like to do it the way its in the code because I could have another file that has the lines that I don't know and the code comparing them would take less time then me looking at the file, counting the lines and putting x lines of getline functions in the code.