How to iterate over the words of a sentence in C++? - c++

Question

My input is "Hello World" and my targeted output is "olleH dlroW".
So my idea is to get the sentence into a variable and then loop over the words in the sentence, reverse each of them and finally concatenate them into a new variable.
My question is: how to iterate over the words of the sentence?
#include <iostream>
#include <stdio.h>
#include <string.h>
using namespace std;
string reverseword(string word)
{
string rword;
int size = word.length();
while (size >= 0)
{
rword+= word[size];
size = size -1;
}
return rword;
}
int main()
{
string sentence;
cout<<"Enter the word/sentence to be reversed: ";
cin >> sentence;
string rsentence;
// for every word in the sentence do
{
rword = reverseword(word);
rsentence = rsentence + " " + rword;
}
cout<<rword;
return 0;
}

Answer 1

Before you can iterate over words in a sentence, you need to read a sentence from input. This line
cin >> sentence;
reads the first word of a sentence, not the whole sentence. Use getline instead:
std::getline(std::cin, sentence);
With sentence in memory, you can iterate it word-by-word using istream_iterator as follows:
stringstream ss(sentence);
for (auto w = istream_iterator<string>(ss) ; w != istream_iterator<string>() ; w++) {
string &word = *w;
...
}
Demo.

Answer 2

Here is a solution that uses find and reverse to achieve the output:
#include <iostream>
#include <string>
#include <algorithm>
int main() {
std::string sentence;
std::getline(std::cin, sentence);
std::cout << sentence << std::endl;
size_t cpos = 0;
size_t npos = 0;
while((npos = sentence.find(' ', cpos)) != std::string::npos)
{
std::reverse(sentence.begin() + cpos, sentence.begin() + npos);
cpos = npos + 1;
}
std::reverse(sentence.begin() + cpos, sentence.end());
std::cout << sentence << std::endl;
return 0;
}
Input:
this is a nice day
Output:
this is a nice day
siht si a ecin yad

Answer 3

for(short i=0;i<sentence.length();i++){
if(sentence[i] == ' '){
counter++;
i++;
}
words[counter] += sentence[i];
}
Note the above loop to split the sentence with space and store it to a string array, words[]
#include <iostream>
#include <stdio.h>
#include <string.h>
using namespace std;
string reverseword(string word) // function to reverse a word
{
string rword;
int size = word.length();
while (size >= 0)
{
rword+= word[size];
size = size -1;
}
return rword;
}
int main()
{
string sentence;
cout << "Enter the word/sentence to be reversed: ";
std::getline(std::cin, sentence);
string rsentence;
string words[100];
string rword;
short counter = 0;
for(short i=0; i<sentence.length(); i++){ // looping till ' ' and adding each word to string array words
if(sentence[i] == ' '){
counter++;
i++;
}
words[counter] += sentence[i];
}
for(int i = 0; i <= counter; i++) // calling reverse function for each words
{
rword = reverseword(words[i]);
rsentence = rsentence + " " + rword; // concatenating reversed words
}
cout << rsentence; // show reversed word
return 0;
}
I have corrected the code. Hope this helps...!!
NB : You were using cin to read space seperated string that is not possible. You must use std::getline(std::cin, sentence) to read space separated strings.
You can also use std::reverse() to reverse a string

Answer 4

Please refer to Most elegant way to split a string?
to split your sentence into tokens(words)
then, iterate over the new list of words to perform any operation

Answer 5

An answers above gives a way to convert your input to words, i.e., cin >> sentence returns a "word" (so, just call it repeatedly).
However, this brings up the question of what is a "word". You would like to translate a computer construct - string of characters - into a more complex form - words. So, you must define what you mean when you want words. It can be as simple as "space" separated substrings or your string - then use the split function, or read your string a word at a time (cin >> word)
Or you may have more stringent requirements, like they can't include punctuation (like a period at the end of a sentence) or numbers. Then think about using Regex and word patterns (like, "\w+").
Or you may want "real" words like you would find in a dictionary. Then you need to take into account your locale, parse your input into chunks (using split, Regex, or something), and look up each chunk in a human language dictionary.
In other words, "word" parsing is only as simple or complex as your requirements are.

Answer 6

With Boost you could use the boost::split function:
#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <boost/algorithm/string.hpp>
int main()
{
std::string sentence = "Hello world";
std::vector<std::string> words;
boost::split(words, sentence, boost::is_any_of(" "));
std::string rsentence;
for (std::string word : words) // Iterate by value to keep the original data.
{
std::reverse(word.begin(), word.end());
rsentence += word + " "; // Add the separator again.
}
boost::trim(rsentence); // Remove the last space.
std::cout << rsentence << std::endl;
return 0;
}

Answer 7

This answer is my humble contribution to the fight against global warming.
#include <string>
#include <iostream>
#include <algorithm>
#include <cctype>
int main()
{
std::string sentence;
while (std::getline(std::cin, sentence))
{
auto ws = sentence.begin();
while (ws != sentence.end())
{
while (std::isspace(*ws)) ++ws;
auto we = ws;
while (we != sentence.end() && !std::isspace(*we)) ++we;
std::reverse(ws, we);
ws = we;
}
std::cout << sentence << "\n";
}
}
This assumes "word" is defined as "a sequence of non-whitespace characters". It is easy to substitute a different character class instead of "non-whitespace", e.g. for alphanumeric characters use std::isalnum. A definition that reflects the real-world notion of word as e.g. used in natural language sciences is far far beyond the scope of this answer.