Creating program to find repeated words in a sentence - c++

Question

I'm having trouble with this project because when I put a sentence such as "cat is not a dog", it will not say "Didn't find repeated word" as intended. Instead, it will say "Found repeated word", as if I it was true. Also, each time it is run for the first time, the first letter is removed from the user input. Why?
#include <iostream>
#include <iomanip>
#include <string>
#include <fstream>
#include <time.h>
#include <stdio.h>
using namespace std;
int main()
{
int count = 0;
bool repeat = false;
char yn;
string input, newWord, firstword;
do
{
count = 0;
repeat = false;
cin.sync();
cout << "Please enter a sentence: ";
cin.ignore();
getline(cin, input);
while (input.at(count) != ' ')
count++;
firstword = input.substr(0, count);
input = input.substr(count++);
count = 0;
while(count < input.size() && repeat == false)
{
count++;
while (count < input.size() && input.at(count) != ' ')
count++;
newWord = input.substr(0, count);
if (firstword.compare(newWord) == 0)
input = input.substr(count++);
else
repeat = true;
}
if (repeat == true)
{
cout << "\nI found a repeated word!";
cout << "\nWould you like to try again? (y/n)";
cin >> yn;
}
else if(repeat == false)
{
cout << "\nI didn't find a repeated word.";
cout << "\nWould you like to try again? (y/n)";
cin >> yn;
}
} while (yn == 'y');
}

Answer 1

You program only checks if the first word is repeated annywhere else in the sentence...
Looking for a repeated word being: Each word must be checked against its immediate predecessor.
You're almost there. You forgot to reassign firstWord to newWord at te end of the parsing loop.
while(count < input.size() && repeat == false)
{
// ...
newWord = input.substr(0, count);
if (firstword.compare(newWord) == 0)
input = input.substr(count++);
else
repeat = true;
firstWord = newWord; // <-- Assign here.
}
Just an aside note, a trick of the trade, if you will.
if (repeat == true)
//...
else if(repeat == false) // <- Avoid doing that. Use plain else for booleans.
A bool can only have two values. And this kind of else if construct will bring unexpected surprises when plain ints are used for boolean equations. (if repeat was 3, which path does each cases of 0, 1, 3 follow?)
Have you tried removing the call to std::cin.sync() ?

Answer 2

Print your input after getline to be sure it's correctly saved. You probably don't need cin.ignore();. The first character is not saved.
An alternative sollution would be to use the following:
#include <iostream>
#include <string>
#include <fstream>
#include <map>
#include <sstream>
using namespace std;
int main()
{
int pos = 0;
string input;
cout << "Please enter a sentence: ";
getline(cin, input);
map<string, int> count_words;
stringstream ss(input);
string word;
while(getline(ss, word, ' '))
count_words[word]++;
map<string, int>::const_iterator it;
for(it = count_words.begin() ; it != count_words.end() ; ++it)
if( it->second == 2)
cout << "Found duplicate: " << it->first << endl;
return 0;
}
this answer(https://stackoverflow.com/a/236803/4388908) provides a good method to split your input.
The rest: Programming Pearls by Jon Bentley