Why is this code not reversing the words in a sentence? - c++

Question

So I want to take the words in a sentence and flip the word, and only the word around. For example:
Hello there
would be changed to:
olleH ereht
So I tried doing so with the following code:
#include <iostream> //Include the necessary header files.
#include <string>
#include <vector>
int main (int argc, const char * argv[]) {
std::string sentence("Hello this is a sentence"); //This is the sentence I want to convert.
char *tokens = strtok(strdup(sentence.c_str()), " "); //Tokenize the sentence.
std::string tempToken; //Will use this to store the tokens in reverse.
std::vector< std::string > strings; //This will keep all contents of the converted sentence.
for (int i = (int)sentence.length()-1; i >= 0; i--) { //Go through the sentence backwards.
if (tokens[i] == NULL) { //If tokens[i] == NULL then that was a complete token.
strings.push_back(tempToken); //Push back the reversed token.
tempToken.clear(); //Clear the reversed token so it can be used again to store another reveresed token.
}
else { //Still in the middle of a token
tempToken.append(&tokens[i]); //Since I am iterating backwards this should store the token backwards...
}
}
for (std::vector<std::string>::reverse_iterator it = strings.rbegin(); it != strings.rend(); ++it) { //Because I used strings.push_back(tempToken) I need to go through the vector backwards to maintain the word placement.
std::cout << *it; //Print the words backwards.
}
}
Basically, I take a sentence. Then I tokenize it. Loop through the string backwards and store the characters in a string until I reach the end of the token. When I reach the end of the token, I take the characters I just stored from looping backwards and put it into a vector. Then after I have done this with all the tokens I print out the contents of the vector.
When I run this program the sentence:
Hello this is a sentence
Gets converted to:
ecenceencetencentenceentencesentence sentencea sentence a sentences a sentenceis a sentence is a sentences is a sentenceis is a sentencehis is a sentencethis is a sentence
What am I doing wrong?

Answer 1

Best to forget everything, and write C++ instead:
#include <string>
#include <sstream>
#include <iostream>
void reverse_words(std::string const & sentence)
{
std::istringstream iss(sentence);
std::string word;
while (iss >> word)
{
std::cout << std::string(word.rbegin(), word.rend()) << " ";
}
std::cout << std::endl;
}

Answer 2

The strtok function doesn't tokenize in one call. It returns the next token each time you call it. Read the documentation more closely.

Answer 3

void main(string s){
List<string> strings = new List<string>();
strings = s.split(" ").toList();
string backwards = "";
foreach(string str in strings){
string stri = str;
for(int i = 0; i< str.length(); i++){
backwards += stri.substr(stri.length() - 1);
stri = stri.substr(0,stri.length() -1);
}
backwards += " ";
}
cout << backwards;
}

Answer 4

This is a well know question with a simple trick (to do it in place):
Reverse the string
For each word
Reverse the word
Try:
#include <iostream>
#include <string>
int main()
{
// Get the line
std::string line;
std::getline(std::cin, line);
// Reverse the whole line.
std::reverse(line.begin(), line.end());
// Find the start of the first word
std::string::size_type beg = line.find_first_not_of(" \t");
while(beg != std::string::npos)
{
// Find the end of the word we have found
std::string::size_type end = line.find_first_of(" \t",beg);
end = (end == std::string::npos ? line.size() : end);
// Reverse the word
std::reverse(&line[beg],&line[end]);
// See if we can find the next word
beg = line.find_first_not_of(" \t", end);
}
// Print the result.
std::cout << line << "\n";
}

Answer 5

try this:
string reverseString(string inputStr){
inputStr += ' ';
int len = inputStr.size();
len--;
int j;
for(int i=0;i<=len;i++){
for( j=i ;inputStr[i] != ' ';i++);
int ii=i;
while(j<=ii){
char temp = inputStr[ii];
inputStr[ii] = inputStr[j];
inputStr[j] = temp;
j++;
ii--;
}
}
return inputStr;
}