String comparision

I'm trying to compare if a string is the same forwards as backwards (for example bob is the same backwards as forwards etc)

I managed to get the string to reverse and store the reverse string in another string variable

However when I try to compare the two I never get the right answer, its always stuck on a false answer.

Code:

---

line = "bob";


        int len = line.length();
        for (int i=0; i<len; i++)
        {
                if (isalnum(line[i]))
                {
                    nospc = nospc + line [i];
                       
                }
       
        }
       
        cleaned = nospc;
        int len2 = nospc.length();
        for (int h=0; h<len2; h++)
        {
                cleaned[h] = tolower(cleaned[h]);
        }
       
        int len3 = cleaned.length();
        for (int x=len3; x>=0; x--)
        {
                lincomp = lincomp + cleaned[x];
        }
        isPali = !cleaned.compare (lincomp);

---

thats the code I'm using, I've also tried the == deal with no success.

Any suggestions?

>> for (int x=len3; x>=0; x--)

len3 is not a valid index into an array (or string in this case). You need to start at len3 - 1.

You should go ahead and use == once you fix that problem, it is clearer. You can also use str += ch instead of str = str + ch.

Thank you so much, that fixed everything!

try it with some standard library algorithms
usestd::string and reverse_copy .

you'll be amazed how easy it is!

Another way is to use the fact that std::string has built-in reverse iterators, which you can pass to the constructor, eg,

Code:

---

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

int main()
{
    string original("hello");
    string backwards(original.rbegin(), original.rend());
    cout << original << " " << backwards << endl;
    cin.get();
}

---

Quote:

---

Originally Posted by ChaosEngine

try it with some standard library algorithms
usestd::string and reverse_copy .

you'll be amazed how easy it is!

---

But you don't learn how to manipulate a string.... ;)

Quote:

---

Originally Posted by WaltP

But you don't learn how to manipulate a string.... ;)

---

yes you do, you just don't learn how to manipulate an array of characters! :D

Code:

---

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

...

string str = "bob";

if( equal(str.begin(),str.begin()+str.length()/2,str.rbegin()) )
    cout << "Equal!" << endl;
else
    cout << "Not equal!" << endl;

---

lol. The master! Minimum number of comparisons noted.