1 безопасность 2к19

#include "pch.h"
#include <string.h>
#include <fstream>
#include <iostream>
using namespace std;

int main()
{
	char mess[1000];
	char messb[1000];
	char alpha[] = "абвгдеёжзийклмнопрстуфхцчшщъыьэюя";
	char alphaB[] = "АБВГДЕЁЖЗИЙКЛМНОПРСТУФХЦЧШЩЪЬЫЭЮЯ";
	char assist[] = " .,-:;^123456789!?";
	int alphabeg = strlen(alpha);
	char codealpha[100];
	char codealphaB[100];
	system("chcp 1251");
	system("cls");
	int zeronumb;
	bool mode = 1;
	bool zeroexists = 1;
	int n = 4, k = 4;
	int nr;
	int target = 0;
	ofstream fout("end.txt");
	ifstream start("start.txt");
	while (!start.eof())
	{
		char buf;
		start.get(messb[target]);
		target++;

	}
	for (int i = 0; i < target - 1; ++i)
	{
		mess[i] = messb[i];
	}
	target--;
	int length = target;
	if (alphabeg%n == 0) { cout << "Error, wrong A key"; }
	else
	{
		for (int i = 2; i < 1000; ++i)
		{
			if (((i*n) % alphabeg) == 1) { nr = i; break; }
		}
		if (mode == 0)
		{
			for (int i = 0; i < length; ++i)
			{
				bool prep = 0;
				int prepn = 0;
				for (int t = 0; t < strlen(assist); ++t)
				{
					if (mess[i] == assist[t])
					{
						prep = 1;
						prepn = t;
					}
				}
				if (!prep)
				{
					for (int j = 0; j < alphabeg; ++j)
					{
						if (mess[i] == alpha[j]) {
							int code = 0;
							code = ((n*j + k) % alphabeg);
							fout << alpha[code];
						}
						else
							if (mess[i] == alphaB[j])
							{
								int code = 0;
								code = ((n*j + k) % alphabeg);
								fout << alphaB[code];
							}
					}
				}
				else
					fout << assist[prepn];
			}
		}
		else
		{
			for (int i = 0; i < length; ++i)
			{
				bool prep = 0;
				int prepn = 0;
				for (int t = 0; t < strlen(assist); ++t)
				{
					if (mess[i] == assist[t])
					{
						prep = 1;
						prepn = t;
					}
				}
				if (!prep)
				{
					for (int j = 0; j < alphabeg; ++j)
					{
						if (mess[i] == alpha[j]) {
							int code = 0;
							code = (nr*(j + alphabeg - k) % (alphabeg));
							fout << alpha[code];
						}
						else
							if (mess[i] == alphaB[j])
							{
								int code = 0;
								code = (nr*(j + alphabeg - k) % (alphabeg));
								fout << alphaB[code];
							}
					}
				}
				else
					fout << assist[prepn];
			}
		}
	}
	system("pause");
	fout.close();
	return 0;
}