Thread: Exercise on Strings

You have a lot of errors in that program syntactic and logical. Here's the fixed program :-)

Code:

#include <iostream.h>
#include <string.h>

int main()
{
	int length;
	int arr1=0;
	typedef char string[30];
	typedef char string2[30];
	string word[10];
	string2 invWord[10];
	cout<<"Enter word"<<endl;
	cin>>word[arr1];
	
	
	while (stricmp(word[arr1], "Quit")!= 0)
	{
		length=strlen(word[arr1]);
		
		for (int j=0, i=length-1; j<length; j++, i--)
		{
   			invWord[arr1][j]=word[arr1][i];
   		}

		invWord[arr1][length] = '\0';

		if (strcmp(word[arr1], invWord[arr1]) == 0)
   			cout<<"Palindrome"<<endl;

   		cout<<"Enter word"<<endl;
   		cin>>word[++arr1];
	}

   	return 0;
}

But you can do a lot better, here's my stab at it :-)

Code:

#include <functional>
#include <algorithm>
#include <iostream>
#include <string>

using namespace std;

class good_char: public unary_function<char, bool> {
  const string good;
public:
  good_char()
    : good("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ")
  {}

  bool operator()(const char c) const
  {
    if (good.find(c) != string::npos)
    {
      return true;
    }

    return false;
  }
};

bool is_palindrome(string& s)
{
  string::iterator new_end = remove_if(s.begin(), s.end(), not1(good_char()));
  s.erase(new_end, s.end());

  string r = s;

  reverse(r.begin(), r.end());

  if (s == r)
  {
    return true;
  }

  return false;
}

int main()
{
  string s;

  cout<<"Enter a word or phrase: ";

  getline(cin, s);

  if (is_palindrome(s))
  {
    cout<<"You entered a palindrome"<<endl;
  }
}

hey cela,
just wanted to make things clear in my head . What does these do?

Code:

class good_char: public unary_function<char, bool> {
  const string good;
public:
  good_char()
    : good(" abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWX
YZ")
  {}

  bool operator()(const char c) const
  {
    if (good.find(c) != string::npos)
    {
      return true;
    }

    return false;
  }
};

>>What does these do?
It's a function object that checks a character given to it with a list of valid characters. If it doesn't match one of those characters then it returns false and remove_if() deletes the character, just what we want. :-)

and hey cela ,
sorry again me here. what does this do??

Code:

string::npos
and lastly why is this empty function?
good_char()
    : good("  abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWX

YZ")
  {//why is it empty here?}

Code:

#include <iostream.h>
#include <string.h>

int main()
{
  int length;
  typedef char string[30];
  typedef char string2[30];
  string word;
  string2 invWord;
  cout<<"Enter word"<<endl;
  cin>>word;

  while (stricmp(word, "Quit")!= 0)
  {
    length=strlen(word);

    for (int j=0, i=length-1; j<length; j++, i--)
    {
      invWord[j]=word[i];
    }

    invWord[length] = '\0';

    if (strcmp(word, invWord) == 0)
       cout<<"Palindrome"<<endl;

    cout<<"Enter word"<<endl;
    cin>>word;
  }

  return 0;
}

> invWord[length] = '\0'

This puts a null terminator at the end of the string - it tells the computer the string's done. word doesn't need one because it has one appended to it when it's read in in the cin statement.

>>Obviously it's going to have a lot less overhead as I've excluded any use of the stl, and it's only 4 lines long
It also doesn't have much flexibility. Since you're making an exact comparison the following palindrome returns false

Code:

a man, a plan, a canal, panama

Oh, yeah. You're right. I didn't take that into consideration. How about this then:

Code:

bool isPalindrome(const char *str) {
  for (int l = 0, r = strlen(str) - 1; l < r; ++l, --r) {
    while (!isalpha(str[l]))
      ++l;
    while (!isalpha(str[r]))
      --r;
    if (l < r && toupper(str[l]) != toupper(str[r]))
      return false;
  }
  return true;
}