Finding palindromes

[Tinnin]

Hello.
I'm doing an exercise whereby I need to test if a word is a palindrome.

My code for the function is as follows:

#include "test_palindrome.h"

using std::string;

bool is_it_palindrome(const string s)
{
    bool palindrome = true;

    for(string::const_iterator iter = s.begin(); iter != s.end(); ++iter)
    {
        string::const_reverse_iterator rit = s.rbegin();
        if(*iter!=*rit)
            palindrome = false;
        ++rit;
    }
    return palindrome;
}

It compiles but when I enter any word, regardless of whether it is a palindrome or not, it comes up as false.

Why is this?

Cheers.

[myk45]

Hi,

string::const_reverse_iterator rit = s.rbegin();

This should be outside the loop(just before the loop). You are creating a new iterator everytime you enter the loop.

PS: This might be an interesting read: Scope of variables

[WaltP]

for(string::const_iterator iter = s.begin(); iter != s.end(); ++iter)What does this line do?

string::const_reverse_iterator rit = s.rbegin();
What does this line do?

What do the variables defined (iter, rit) point to or indicate.

Why make pointer to the characters? Why not generate subscripts and just use them?

[vijayan121]

string::const_reverse_iterator rit = s.rbegin();
This should be outside the loop(just before the loop)

Yes.

And you need not go all the way to end(); upto the middle of the string would suffice.

Which would make the code equivalent to:

bool is_palindrome( const std::string& str )
{ return std::equal( str.begin(), str.begin() + str.size()/2, str.rbegin() ) ; }

http://en.cppreference.com/w/cpp/algorithm/equal

[Tinnin]

Thanks myk45. I should have seen that. \sigh.

In re WaltP's post; The reason I took this approach was because the chapter of "Accelerated C++" was all about iterators and seemed to want me to go down this path.

Thanks for the help guys.

[WaltP]

In re WaltP's post; The reason I took this approach was because the chapter of "Accelerated C++" was all about iterators and seemed to want me to go down this path.

OK. That makes sense.