Определить маску подсети — C++

Разработать приложение, которое по заданному классу (А, В или С), количеству подсетей N и максимальному количеству компьютеров М в подсети определяет маску для разбиения на подсети и список возможных IP-адресов подсетей. Если разбиение на подсети невозможно, приложение должно выдавать соответствующее сообщение об ошибке.

#define _CRT_SECURE_NO_WARNINGS

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <iostream>

using namespace std;


typedef struct _TAddress
{
	char IPclass;
	int a[4];
	int freeBits;
	int Nbits;
	int Mbits;
}   TAddress;

void FillPow2(int pow2[])
{
	int i = 0;
	pow2[0] = 1;
	while (++i<25)
		pow2[i] = pow2[i - 1] * 2;
}

int IsClass(char c)
{
	char *alphabet = "ABC";
	int i = strlen(alphabet);
	while (--i >-1)
		if (c == alphabet[i])
			return 1;
	return 0;
}

TAddress *CreateAddress(char cl)
{
	TAddress *address = (TAddress*)malloc(sizeof(TAddress));
	address->IPclass = cl;
	address->a[0] = 255;
	address->a[1] = address->a[2] = address->a[3] = 0;

	if (cl == 'A')
		address->freeBits = 24;
	else
	{
		address->a[1] = 255;
		if (cl == 'B')
			address->freeBits = 16;
		else
		{
			address->a[2] = 255;
			address->freeBits = 8;
		}
	}
	address->Mbits = address->Nbits = -1;

	return address;
}

void DeleteAddress(TAddress *address)
{
	free(address);
}

void PrintAddress(TAddress *address)
{
	for (int i = 0; i<4; i++)
		printf("%3d.", address->a[i]);
	printf("\n");
}

void FillBits(TAddress *address, int N, int M, int pow2[])
{
	int i;
	if (N)
	{
		for (i = 0; i<25; i++)
			if (N <= pow2[i] - 2)
			{
				address->Nbits = i;
				break;
			}
		for (i = 0; i<25; i++)
			if (M <= pow2[i] - 2)
			{
				address->Mbits = i;
				break;
			}
	}
	else
	{
		address->Nbits = 0;
		address->Mbits = address->freeBits;
	}
}

int CheckBits(TAddress *address)
{
	return address->Nbits + address->Mbits <= address->freeBits && address->Nbits >= 0 && address->Mbits>0;
}

int ai(int pow2[], int bits)
{
	int i = 0, sum = pow2[7];
	while (++i < bits)
		sum += pow2[7 - i];
	return sum;
}

void CreateMask(TAddress *address, int pow2[])
{
	if (!address->Nbits)
		return;
	if (address->IPclass == 'C')
	{
		address->a[3] = ai(pow2, address->Nbits);
		return;
	}
	if (address->IPclass == 'B')
	{
		if (address->Nbits <= 8)
		{
			address->a[2] = ai(pow2, address->Nbits);
			return;
		}
		else
		{
			address->a[2] = 255;
			address->a[3] = ai(pow2, address->Nbits - 8);
			return;
		}
	}
	if (address->Nbits <= 8)
	{
		address->a[1] = ai(pow2, address->Nbits);
		return;
	}
	else if (address->Nbits <= 16)
	{
		address->a[1] = 255;
		address->a[2] = ai(pow2, address->Nbits - 8);
		return;
	}
	else
	{
		address->a[1] = address->a[2] = 255;
		address->a[3] = ai(pow2, address->Nbits - 16);
		return;
	}
}


int main()
{
	setlocale(LC_ALL, "Russian");
	int pow2[25], N, M;
	FillPow2(pow2);
	char cl;

	do
	{
		printf("Класс сети:\t");
		cl = toupper(getc(stdin));
		getc(stdin);
	} while (!IsClass(cl));

	TAddress *address = CreateAddress(cl);
	printf("Класс стандарт маски:\t");
	PrintAddress(address);

	printf("\n\nКоличество подсетей N = ");
	scanf("%d", &N);
	printf("Максимально количество компьютеров M = ");
	scanf("%d", &M);
	getc(stdin);

	FillBits(address, N, M, pow2);
	printf("Free bits: %d\tBits for subs: %d\tBits for comps: %d", address->freeBits, address->Nbits, address->Mbits);
	if (CheckBits(address))
	{
		CreateMask(address, pow2);
		printf("\n\nМаска для данной подсети:\t");
		PrintAddress(address);
	}
	else
		printf("\n\n\Невозможно создать эту конфигурацию\n");

	DeleteAddress(address);
	getchar();
	return 0;
}