Неразрешённый внешний элемент

https://pastebin.com/tjRGPNkq

#include <ctype.h>
#include <vector>
#include <iostream>
#include <iterator>
#include <string>
using namespace std;
char arr_en[5][5];
char arr_ru[4][8];

int request() {
setlocale(LC_ALL, "Russian");
string req;
cout << "какой язык вы выбираете? \n";
cin >> req;

if (req == "ru") int main_ru();
if (req == "en") int main_en();
else {
cout << "Не могу иденфицировать выбранный язык";
}
return 0;
}


int has_duplication_en(char letter) {
int i, j;
int size = sizeof(arr_en) / sizeof(arr_en[0]);
int result = 0;
for (i = 0; i < 5; i++) {
for (j = 0; j < 5; j++) {
result = (int)letter ^ (int)arr_en[j];
if (result == 0) return 1;
}
}
return 0;
}


int main_en() {
setlocale(LC_ALL, "Engish");
int i, j;
char letters[] = { 'K', 'E', 'Y', 'W', 'O', 'R', 'D', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I' ,'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z' };
char key[] = { 'K', 'E', 'Y', 'W', 'O', 'R', 'D' };

vector<char> plain;
vector<char> cipher_text;
char c;
char pre_char;
pre_char = ' ';
printf("Enter plain text to encrypt: \n");
while (c = getchar()) {
if (c == '\n' || c == '\0') break;
c = toupper(c);
if (c != ' ') { // we do not consider spaces
if (c == 'J') c = 'I';
if (pre_char == c) {
plain.push_back('X');
plain.push_back(c);
}
else {
plain.push_back(c);
}
pre_char = c;
}
}
// if length of key array is odd, we add 'X' to the end of key
if (plain.size() % 2 == 1) {
plain.push_back('X');
}

// filling array with key and letters of alphabet
int m = 0;
for (i = 0; i < 5; i++) {
for (j = 0; j < 5; j++) {
while (has_duplication_en(letters[m])) {
m++;
}
arr_en[j] = letters[m];
}
}

// encrytion
int n = 0;
int first_i, first_j, second_i, second_j;
while (n < plain.size()) {
for (i = 0; i < 5; i++) {
for (j = 0; j < 5; j++) {
if (arr_en[j] == plain.at(n)) {
first_i = i;
first_j = j;
}
if (arr_en[j] == plain.at(n + 1)) {
second_i = i;
second_j = j;
}
}
}
// if both two letters are in the same row
if (first_i == second_i) {
cipher_text.push_back(arr_en[first_i][(first_j + 1) % 5]);
cipher_text.push_back(arr_en[second_i][(second_j + 1) % 5]);
}

// if both two letters are in the same column
else if (first_j == second_j) {
cipher_text.push_back(arr_en[(first_i + 1) % 5][first_j]);
cipher_text.push_back(arr_en[(second_i + 1) % 5][second_j]);
}
// otherwise we consider the rectangle that they form
else {
cipher_text.push_back(arr_en[first_i][second_j]);
cipher_text.push_back(arr_en[second_i][first_j]);
}
n += 2;
}


// result : ecnrypted message
printf("Encrypted message: \n");
std::copy(cipher_text.begin(), cipher_text.end(), std::ostream_iterator<char>(std::cout, " "));
printf("\n");



// demonstration
printf("Playcipher Matrix: \n");
for (i = 0; i < 5; i++) {
for (j = 0; j < 5; j++) {
printf("%c ", arr_en[j]);
}
printf("\n");
}
return 0;
}


int has_duplication_ru(char letter) {
int i, j;
int size = sizeof(arr_ru) / sizeof(arr_ru[0]);
int result = 0;
for (i = 0; i < 5; i++) {
for (j = 0; j < 5; j++) {
result = (int)letter ^ (int)arr_ru[i][j];
if (result == 0) return 1;
}
}
return 0;
}


int main_ru() {
setlocale(LC_ALL, "Russian");
int i, j;
char arr_ru[4][8];
char letters[] = { 'К', 'Ю', 'Ч', 'А', 'Б', 'В', 'Г', 'Д', 'Е', 'Ё', 'Ж', 'З', 'И', 'Й', 'К', 'Л' ,'М', 'Н', 'О', 'П', 'Р', 'С', 'Т', 'У', 'Ф', 'Х', 'Ц', 'Ч', 'Щ', 'Ъ', 'Ы', 'Ь','Э','Ю','Я' };
char key[] = { 'К', 'Л', 'Ю', 'Ч' };

vector<char> plain;
vector<char> cipher_text;
char c;
char pre_char;
pre_char = ' ';
printf("Введите текст, который надо закодировать: \n");
while (c = getchar()) {
if (c == '\n' || c == '\0') break;
c = toupper(c);
if (c != ' ') { // we do not consider spaces
if (c == 'Ё') c = 'Е';
if (pre_char == c) {
plain.push_back('Х');
plain.push_back(c);
}
else {
plain.push_back(c);
}
pre_char = c;
}
}
// if length of key array is odd, we add 'X' to the end of key
if (plain.size() % 2 == 1) {
plain.push_back('Х');
}

// filling array with key and letters of alphabet
int m = 0;
for (i = 0; i < 4; i++) {
for (j = 0; j < 8; j++) {
while (has_duplication_ru(letters[m])) {
m++;
}
arr_ru[i][j] = letters[m];
}
}

// encrytion
int n = 0;
int first_i, first_j, second_i, second_j;
while (n < plain.size()) {
for (i = 0; i < 4; i++) {
for (j = 0; j < 8; j++) {
if (arr_ru[i][j] == plain.at(n)) {
first_i = i;
first_j = j;
}
if (arr_ru[i][j] == plain.at(n + 1)) {
second_i = i;
second_j = j;
}
}
}
// if both two letters are in the same row
if (first_i == second_i) {
cipher_text.push_back(arr_ru[first_i][(first_j + 1) % 4]);
cipher_text.push_back(arr_ru[second_i][(second_j + 1) % 8]);
}

// if both two letters are in the same column
else if (first_j == second_j) {
cipher_text.push_back(arr_ru[(first_i + 1) % 4][first_j]);
cipher_text.push_back(arr_ru[(second_i + 1) % 8][second_j]);
}
// otherwise we consider the rectangle that they form
else {
cipher_text.push_back(arr_ru[first_i][second_j]);
cipher_text.push_back(arr_ru[second_i][first_j]);
}
n += 2;
}


// result : ecnrypted message
printf("Зашифрованное сообщение: \n");
std::copy(cipher_text.begin(), cipher_text.end(), std::ostream_iterator<char>(std::cout, " "));
printf("\n");



// demonstration
printf("Матрица Плейфера: \n");
for (i = 0; i < 4; i++) {
for (j = 0; j < 8; j++) {
printf("%c ", arr_ru[i][j]);
}
printf("\n");
}
return 0;
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