How do I split a user-defined sentence into words in C++ using substr and find?

Question

I used this function but it is wrong.

for (int i=0; i<sen.length(); i++) {
    if (sen.find (' ') != string::npos) {
        string new = sen.substr(0,i);
    }
cout << "Substrings:" << new << endl;
}

Thank you! Any kind of help is appreciated!

Answer 1

new is a keyword in C++, so first step is to not use that as a variable name.

After that, you need to put your output statement in the "if" block, so that it can actually be allowed to access the substring. Scoping is critical in C++.

Answer 2

First: this cannot compile because new is a language keyword.

Then you have a loop running through every character in the string so you shouldn't need to use std::string::find. I would use std::string::find, but then the loop condition should be different.

Answer 3

No need to iterate over the string, find already does this. It starts to search from the beginning by default, so once we found a space, we need to start the next search from this found space:

std::vector<std::string> words;

//find first space
size_t start = 0, end = sen.find(' ');

//as long as there are spaces
while(end != std::string::npos)
{
    //get word
    words.push_back(sen.substr(start, end-start));

    //search next space (of course only after already found space)
    start = end + 1;
    end = sen.find(' ', start);
}

//last word
words.push_back(sen.substr(start));

Of course this doesn't handle duplicate spaces, starting or trailing spaces and other special cases. You would actually be better off using a stringstream:

#include <sstream>
#include <algorithm>
#include <iterator>

std::istringstream stream(sen);
std::vector<std::string> words(std::istream_iterator<std::string>(stream), 
                               std::istream_iterator<std::string>());

You can then just put these out however you like or just do it directly in the loops without using a vector:

for(std::vector<std::string>::const_iterator iter=
    words.begin(); iter!=words.end(); ++iter)
    std::cout << "found word: " << *iter << '\n';

Answer 4

This doesn't use substr and find, so if this is homework and you have to use that then this won't be a good answer... but I do believe it's the better way to do what you're asking in C++. It's untested but should work fine.

//Create stringstream and insert your whole sentence into it.
std::stringstream ss;
ss << sen;

//Read out words one by one into a string - stringstream will tokenize them
//by the ASCII space character for you.
std::string myWord;
while (ss >> myWord)
    std::cout << myWord << std::endl;  //You can save it however you like here.

If it is homework you should tag it as such so people stick to the assignment and know how much to help and/or not help you so they don't give it away :)