Using binary search on a vector of strings

[WesleySnipes]

I am trying to create a spell checker program. I load and sort a 480,000 word document into a vector. Now, I ask the user what word to spell check. I want to use a binary search to see if the word is in the dictionary. The problem is: I don't know how to use binary search for a vector. I have used it before with an array but can't seem to make it work with a vector. Here's my program:

#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <algorithm>

using namespace std;

int main(int argc, char *arg[] )
{
    
    string wordToTest;
    cout << "word to spell check?";
    cin >>wordToTest;
    
    //temp storage for each word
    string word;
    vector<string> dictionary;
    //read the dictionary file
    ifstream readFile("Words.txt");
    //while there is a word, put it into the vector
    while(getline(readFile, word, '\n'))
    {
        dictionary.push_back(word);
    }
    readFile.close();
    sort(dictionary.begin(), dictionary.end());
    
    //binary search here


return 0;
}

Now, I want to use this algorithm but make it work for a vector.

int binarySearch(int sortedArray[], int first, int last, int key) {
    
   while (first <= last) {
       int mid = (first + last) / 2;  // compute mid point.
       if (key > sortedArray[mid]) 
           first = mid + 1;  // repeat search in top half.
       else if (key < sortedArray[mid]) 
           last = mid - 1; // repeat search in bottom half.
       else
           return mid;     // found it. return position /////
   }
   return -(first + 1);    // failed to find key
}

My first attempt was to change every array to vector but it didn't work. You don't have to write it for me just help me out, thanks!