проверяй.cpp

#include "stdafx.h"
#include <iostream>
using namespace std;

#define STR_LEN 81

bool sameStrings(char* first, char* second, int firstLen, int secondLen) {
	if (firstLen != secondLen)
		return false;

	for (int i = 0; i < firstLen; i++)
		if (first[i] != second[i])
			return false;

	return true;
}

int main()
{
	system("chcp 1251 > nul");

	char* input = new char[STR_LEN];
	char* fixedInput = new char[STR_LEN];
	char* lastWord = new char[STR_LEN];
	char* curWord = new char[STR_LEN];

	int posFI = 0;
	int posLW = 0;
	int posCW = 0;
	cout << "Введите текст (только латинские строчные буквы и пробелы, в конце - точка): " << endl;
	cin.getline(input, STR_LEN);

	while (*input && *input != '.') {
		if (*input >= 'a' && *input <= 'z') {
			fixedInput[posFI++] = *input;
			lastWord[posLW++] = *input;
		}
		else if (*input == ' ') {
			posLW = 0;
			if (posFI > 0 && fixedInput[posFI - 1] != ' ')
				fixedInput[posFI++] = ' ';
		}

		*input++;
	}

	fixedInput[posFI] = '\0';
	bool needSpace = false;

	cout << "Результат: ";
	while (true) {
		if (*fixedInput >= 'a') {
			curWord[posCW++] = *fixedInput;
		}
		else {
			if (!sameStrings(curWord, lastWord, posCW, posLW)) {
				curWord[posCW] = '\0';
				char* buf = curWord;
				bool used[256] = { 0 };

				if(needSpace)
					cout << ' ';
				while (*buf != '\0') {
					if (*buf >= 'a' && *buf <= 'z') {
						if (!used[*buf]) {
							cout << *buf;
							used[*buf] = true;
						}
					}
					else if (*buf == ' ' && (*(buf - 1) != ' ')) {
						cout << ' ';
						memset(used, 0, 256 * sizeof used[0]);
					}
					buf++;
					needSpace = true;
				}
			}

			if (*fixedInput == '\0')
				break;

			posCW = 0;
		}

		*fixedInput++;
	}
	lastWord[posLW] = '\0';

	system("pause > nul");
	return 0;
}