Help with strings in a recursive string reversal program

[Kyle Willett]

I'm doing a program that is supposed to reverse a string entered my the user using a recursive function, I almost have it solved except for one little elusive bug that I can not understand.

//******************************************************************************
//Programer: Kyle Willett
//Course:    CS-1513
//Program:   3 exercise 7 page 933.
//Purpose:   Reverse the contents of a string.
//Input:     A string.
//Calculate: The reverse of the inputed string.
//Output:    The user intputed string, and the reversed string.
//******************************************************************************

#include<iostream>
#include<string>
#include<cstdlib>

using namespace std;

//******************************************************************************
//function prototypes
void input(string &stringInput, int &size);
//This function gets a string from the user.

void fillReverse(string &reversed, int size);
//This function was not part of the original design, it proved neccesary because
//the reversed string in main would not work in the reverse function unless it
//had been initilized to some value, and becuse it is not know what size the 
//user string is until entered the reversed string cann't be intitilized in main
//so this function is used to fill it with random values for the same size of
//the user entered string.

void output(string userStringOut, string reversedStringOut);
//This function outputs the user string and the reversed string.

void reverseString(string userString, string &reversedString, int size);
//This function recursivly calculates the reverse of a string.

//******************************************************************************
//******************************************************************************
int main()
{
    string userString;
    string reversed;
    //The two string variables for the reversing operation.
    
    cout << endl << reversed << endl;
    
    int size=0;
    
    input(userString, size);
    
    fillReverse(reversed ,size);
    
    reverseString(userString, reversed, size-1);
    
    output(userString, reversed);
    
    return 0;
}
//******************************************************************************
//******************************************************************************
//function implimentations

void input(string &stringInput, int &size)
{
    cout << "Please enter a string you would like to see reversed." << endl;
    cout << "Enter a string: ";
    cin >> stringInput;
    cout << endl << endl;
    
    size=stringInput.length();
    //This function gets the length of the string for use in the
    //recursive function.
}
//******************************************************************************
void output(string userStringOut, string reversedStringOut)
{
    cout << "The contents of the string you entered is: ";
    cout << userStringOut;
    cout << endl;
    cout << "The contensts of the reversed string is: ";
    cout << reversedStringOut;
    cout << endl << endl;
}
//******************************************************************************
void reverseString(string userString, string &reversedString, int size)
{
    char temp;
    static int n;
    
    if(size >= 0)
    {
        temp=userString[n];
        reversedString[size]=temp;
        n++;
        reverseString(userString, reversedString, size-1);
    }
}
//******************************************************************************
void fillReverse(string &reversed, int size)
{
    char fillLetter=65;
    
    for(int n=0; n< size; n++)
    {
        reversed[n]=fillLetter;
    }
}
//******************************************************************************

On line 41 if I supply a stating value for the reversed string that is the same size as the one I input for example "AAAA" and I input "test" the program outputs "tset" which is correct, but as it is with no starting value for the reversed string the program doesn't output a value for the reversed string. To solve this I tried to write the fillReverse function but this didn't solve the problem.

I tried running this program on my local windows xp computer from the command line and the school I go to student unix server and got the same result.

Any help on why the string has to have an initial value and ways to solve the problem would be appreciated. Thanks.

[Narue]

Hmm, I'd say that a good solution is to rewrite your reverseString() entirely so that it builds the reversed string rather than tries to fill a caller provided object:

#include <iostream>
#include <string>

using namespace std;

string reverseString(string::const_iterator first, string::const_iterator last)
{
    if (first == last)
        return string();

    return reverseString(first + 1, last) + *first;
}

int main()
{
    string userString;

    cout << "Please enter a string you would like to see reversed." << '\n';
    cout << "Enter a string: ";
    
    if (getline(cin, userString)) {
        string reversed = reverseString(userString.begin(), userString.end());
        
        cout << "The contents of the string you entered is: " << userString << '\n';
        cout << "The contensts of the reversed string is: " << reversed << '\n';
    }
}

Greatly simplified, no?

[Kyle Willett]

Thanks for the help. though I kept on working on solving it and eventially came up with the solution using the line

reversed=userString;

in side the main function and remove the fillReverse function. This way the reverse array is already the correct size when it reaches the reverseString function.