Problems with palindrome...still

[afleury1]

I have posted thins one once before, but It seems I am not able to resolve a couple of problems with my program.

1. Palindrome option is not working in the sense that:
when user enter option 2 (find if it is palindrome)
user enter: Madam
result is: This is not a palindrome

2. when user chooses option 2 three times in row:
input:2
in put: Madam
output: is not a palindrome
do you want to try again?
input: yes
The program goes into an infinite loop of the following:
Enter a word or sentence I will check if it is a palindrome:
input:2
input: Madam
output: is not a palindrome
do you want to try again?

  #include<iostream>
#include<string>
#include<ctype.h>
#include<stdio.h>
using namespace std;

//prototype of functions
bool is_palindrome(string&, int, int);
string Reverse(string, string);
string remove_char(string);

int main()
{

//variable declarations
string userInput;
string sentence2;
int first = 0;
size_t last = string::npos;
int userchoice;
string reversed,r;
locale loc;
string answer;

//Loop to keep program running until user quits
do
{
//Reverse function
cout<< "Do you want to reverse a string (1), determine if it is a palindrome(2) or quit:" << endl;
cin >> userchoice;
cout<< userchoice<< endl;
cin.ignore(80,'\n');


if (userchoice ==1)
{
cout<< " Please enter a word or sentence, I will reverse it:" <<endl;
getline(cin, userInput);


cout<< Reverse(userInput, reversed) << " is reversed." << endl;
}

//palindrome function
if (userchoice ==2)
{
cout<< " Please enter a word or sentence, I will determine if it is a palindrome or not:" <<endl;
cin>>userInput;


// the upper to lowercase
string str= userInput;
for (size_t i=0; i<str.length(); ++i)
     str[i] = tolower(str[i]);

sentence2 = remove_char(str);

cout<< (is_palindrome(sentence2, first, last) ? " is a palindrome." : " is not a palindrome.") << endl;
cin.get();
}
cout<< "Do you want to try again ('yes' or 'no'): " << endl;
cin>> answer;

}while (answer == "yes");
return 0;
}


//Functions

// remove non letters
string remove_char(string userInput)
{
        string sentence2;

        for (unsigned int x=0; x < userInput.length(); x++)
        {
                if (isalnum(userInput[x]))
                {
                        sentence2 += userInput[x];

                }
        }
        return sentence2;
}


// return true if palindrome
bool is_palindrome(string& sentence2, int first = 0, int last = string::npos)
{
if(last == string::npos)
{
last = (sentence2.length()-1);
}
if (sentence2[first] == sentence2[last])
{
if ((first-last)== 0)
{
return true;
}
else if (first ==(last-1))
{
return true;
}
else
{
return is_palindrome(sentence2, first+1, last-1);
}
}
else
{
return false;
}
}


// reverse string
string Reverse(string word, string reversed)
{
if(word.length() == 0)
{
return reversed;
}
else
{
string temp;
reversed = word.substr(0,1) + reversed;
temp = word.substr(1);
return Reverse(temp, reversed);
}
}

**sorry the indentation didn't transfer over properly

[Stewbond]

Does "madam" return true even if "Madam" does not?

I admit that I was hesitant to answer this one as chains of if-elseif-else statements make me nauseous. This type of programming is very prone to typos or un-considered cases which will really kill you. If possible, it's best to use a single statement that will do the work for you.

Your is_palindrome() function will be so easy if it uses the Reverse() function:

std::string Reverse(std::string str)
{
    if (str.size() == 0)  return str;

    // Return the last letter   + reverse( string without last letter )
    return str.at(str.size()-1) + Reverse( str.substr(0, str.size()-1) );
}

bool is_palindrome(const std::string str)
{
    return str == Reverse(str);
}

Hold on while I try to simplify your main, and make this case insensitive

[Stewbond]

Here's what I managed to get for you. I re-implemented toupper() from <cctype> because I was having troubles with the const-correctness. Otherwise, I kept each function with as small of a scope as possible. And I used Reverse() in the is_palidrome() function.

I've checked palindrome sentences such as "rise to vote sir" and "loin oil" and this all checked out ok.

I tried to keep with your recursive theme, but strayed from this in the "RemoveSpaces" function which was added to support sentences. For your problems with infinite loops, these I think were caused by using cin >> instead of getline. Honestly, I don't use cin in any of my applications, but the >> operator assumes that you know exactly what is coming in which can mess up when you press enter or spacebar.

I also kept your variables in as small a scope as possible. I suppose that's a matter of personal preference. In C, we had to declare everything at the start, but in C++ it can be done in a smaller scope. Some people are used to declaring it at the start, but I HATE scrolling up to figure out how something what declared. I also find that people add variables, forget about them, then eventually remove the usage without removing the variable. Lots of garbage ends up at the top of each function.

#include <string>
#include <cstdlib>
#include <iostream>
using namespace std;

char toupper(char c)
{
    if(c >= 'a' && c <= 'z')   c += ('A' - 'a');
    return c;
}

string ToUpper(string str)
{
    if (str.size() == 0) return str;
    return toupper(str.at(0)) + ToUpper( str.substr(1, str.size()-1) );
}

string RemoveSpaces(string str)
{
    string::iterator it = str.begin();

    while (it != str.end())
    {
        if (*it == ' ' || *it == '\t' || *it == '\n' || *it == '\r')
            it = str.erase(it);
        else
            ++it;
    }
    return str;
}

string Reverse(string str)
{
    if (str.size() == 0)  return str;
    return str.at(str.size()-1) + Reverse( str.substr(0, str.size()-1) );
}

bool is_palindrome(string str)
{
    str = ToUpper(str); // Case insensitive
    str = RemoveSpaces(str); // removes whitespace for the sentences
    return str == Reverse(str);
}

int main()
{
    string again;
    do
    {
        string input;

        cout<< "Do you want to reverse a string (1), determine if it is a palindrome(2) or quit:" << endl;
        getline(cin,input);
        int choice = atoi(input.c_str());

        if (choice ==1)
        {
            cout<< " Please enter a word or sentence, I will reverse it:" <<endl;
            getline(cin, input);

            cout<< "The reverse of " << input << " is " << Reverse(input) << endl;
        }
        else if (choice ==2)
        {
            cout<< " Please enter a word or sentence, I will determine if it is a palindrome or not:" <<endl;
            getline(cin, input);

            cout<< input << (is_palindrome(input) ? " is" : " is not") << " a palindrome." << endl;
        }

        cout<< "Do you want to try again ('yes' or 'no'): " << endl;
        getline(cin, again);

    }while (again[0] == 'y' || again[0] == 'Y');
    return 0;
}

[afleury1]

Thanks so much for you help on this one. I really appreciate it.