Thread: Palindrome-kinda program with pointers

I am writing a program and I need some help. I need to know how to analyze a string, and then word by word reverse the order of that string. For example:

User Input: Hello to the world!
Program Output: olleH ot eht !dlrow

First problem: I need the program to read the string word by word, and sort of isolate each word. How do I do this?!

Second problem: After isolating each word, I would like to use a pointer variable that assigned to the first character, and then a pointer variable that is assigned to the last character of the SAME word, and then switch those. Continue for all the words in the entire string, like my example above.

NOTE: I know there are reverse(), begin(), and end() member functions, but I do not want to do that. I want to MANUALLY do this through my program. Thanks for the help!

sounds good, thanks. OK, well, here I have a part of my main() function, but I cannot determine how to split up my string word by word. I know how to reverse the whole thing, but I really cannot get much farther than that.

Code:

string input;
char *first, *last;
cout << "Enter the string you want to reverse: ";
getline(cin, input);
for (int i = (input.size() - 1); i >= 0; i--)
        cout << input[i];

*first should address the first character in the word, and *last should address the last character in the word. Thanks for the help in advance!

here is a new version of the code: however i am problem with this run-time error, i believe. when i run the program (perfectly compiled and no errors), it basically opens up the program and then closes it immediately. maybe you might know what is wrong with it. thanks for the help. I think i may have captured what you meant in your last post...

Code:

string input, word;
  char *front, *rear; 
  vector <string> string; // This will hold the individual words temporarily until they are replaced
 
  cout << "Enter a sentence that you would like to reverse: ";
  getline(cin, input);
 
  // Puts the string into a stream
  istringstream break_apart(input);
 
  while (break_apart >> word)
  {
    *front = word.at(0);
    cout << *front;
    *rear = word.at(word.size() - 1);
    cout << *rear;
    string.push_back(word);
  }

the error has to come from the pointer references towards the end. but why?!

Ok, now I'm in another rut. I understand how to search the word and then switch the first and last characters, working inwards. But I do not know how to put the whole word together. If I inputted "Hello", I would expect the program to output "olleH." The way I have it, my program outputs "oH le l." How do I achieve the expected way?!? Here is the main part of my code. Thank you very much for all the help to everyone on this post!!!

Code:

istringstream break_apart(input);
 
  while (break_apart >> word)
  {
    
       for (int i = 0; i < (word.size() / 2); i++)
       {
           front = &word.at(i);
           rear = &word.at(word.size() - 1 - i);
           
           char temp = *front;
           *front = *rear;
           *rear = temp;
           cout << *front << " " << *rear << " ~ ";
       }
      
    string.push_back(word);
  }

I commented out the line, but it still isn't working. maybe i'm not understanding what you're saying...

Can you tell me how to permanently change a character, so that when I output 'word' after my search/palindromesque loop it outputs "olleH". Like I said I uncommented that print line like you said, and then I outputted 'word' after my loop and it printed "Hello."

Thanks for the help!

Why are you using istringstream? cin itself is a stream; you can do the same with that as you're doing with the istringstream.

Something like this. I realize that my first for loop will not capture all of the characters. It misses the middle one. But run this, and you'll see what I mean that I cannot get the "olleH" way. Thank you very much!

Code:

#include <iostream>
#include <sstream>
#include <string>
#include <vector>  
void swap (char *front, char *rear); 
using namespace std;
 
int main()
{
  string input, word;
  char *front, *rear; 
  vector <string> string; // This will hold the individual words temporarily until they are replaced
 
  cout << "Enter a sentence that you would like to reverse: ";
  getline(cin, input);
 
  // put the sentence into a stream
  istringstream break_apart(input);
 
  while (break_apart >> word)
  {
     if (word.size() % 2)
    {
       for (int i = 0; i < (word.size() / 2); i++)
         {
             front = &word.at(i);
             rear = &word.at(word.size() - 1 - i);
             
             swap(*front, *rear);
             cout << *front << " " << *rear << " - ";
         }
    }
    else 
         for (int i = 0; i < (word.size() / 2); i++)
         {
             front = &word.at(i);
             rear = &word.at(word.size() - 1 - i);
           
             swap(*front, *rear);
             cout << *front << " " << *rear << " - ";
         }
    string.push_back(word); 
  }  

  return 0;
}
void swap (char *front, char *rear)
{
     char temp = *front;
     *front = *rear;
     *rear = temp;
}

OK, so I figured out my problem to the last part. Thank you Sebastiani for the help! However, how do I store my modified string into a dynamic array for future use so that I can output it later on in the program?

Also, if I wanted to, instead of switching all of the letters around in each word, switch all of the words in string (using the same kinda method), how would I go about doing this?