Caesar with args parameters bribro

#include <fstream>
#include <iostream>
#include <vector>

char encode(char c, int key) {
  std::vector<char> alphabet = {'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I',
                                'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R',
                                'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z'};
  return alphabet[((c - 65) + key) % (alphabet.size())];
}

char decode(char c, int key) { return encode(c, 26 - key); }

std::string full_decode(std::string s, int key) {
  for (int i = 0; i < s.length(); i++) {
    if (s[i] != ' ')
      s[i] = decode(s.at(i), key);
  }

  return s;
}

std::string full_encode(std::string s, int key) {
  for (int i = 0; i < s.length(); i++) {
    if (s[i] != ' ')
      s[i] = encode(s.at(i), key);
  }

  return s;
}

// (A B C D E F G H I J K L M N O P Q R S T U V W X Y Z)
// (0 1 2 3 4                                        25)
int main(int argc, char **args) {
  using namespace std;

  if(argc != 2) {
    cout << "Utilizzo del programma: crypta.exe nomefile.txt" << endl;
    return -1;
  }

  ofstream fout;
  ifstream fin;
  fin.open(args[1]);
  fout.open("output.txt");

  string file_input = "";

  while (!fin.eof()) {
    string temp;
    fin >> temp;
    file_input += temp + " ";
  }

  string s = full_encode(file_input, 7);
  // cout << endl << s << endl;
  // s = full_decode(s, 7);
  // cout << endl << s << endl;
  fout << s;
  fout.close();
  return 0;
}