A program to find out if a word is palindrome - c++

Question

Written some algorithm to find out if a given word is a palindrome. But one of my variables (counter) seems not updating when I debugged and I can't figure out what is wrong with it. I may be wrong though... any help will be needed as I don's wanna copy some code online blindly.
Below is the code:
#include <iostream>
#include <cstring>
using namespace std;
int main(){
//take input
string input;
cout << "Enter your word: ";
cin >> input;
//initialize arrays and variables
int counter = 0, k = 0;
int char_length = input.length();
char characters[char_length];
strcpy(characters, input.c_str());//copy the string into char array
//index of character at the midpoint of the character array
int middle = (char_length-1)/2;
int booleans[middle]; //to keep 1's and 0's
//check the characters
int m = 0, n = char_length-1;
while(m < middle && n > middle){
if(characters[m] == characters[n]){
booleans[k] = 1;
} else {
booleans[k] = 0;
}
k++;
m++;
n--;
}
//count number of 1's (true for being equal) in the booleans array
for(int i = 0; i < sizeof(booleans)/sizeof(booleans[0])-1; i++){
counter += booleans[i];
}
//compare 1's with size of array
if(counter == middle){
cout << input << " is a Palindrome!" << endl;
} else {
cout << input << " is not a Palindrome!" << endl;
}
return 0;
}

Answer 1

Brother it seems difficult to understand what your question is and what code you are typing. I am not very much experienced but according to me palindrome is a very very simple and easy program and i would have wrote it as:
#include <iostream>
#include <string.h>
using namespace std;
int main()
{
char str1[20], str2[20];
int i, j, len = 0, flag = 0;
cout << "Enter the string : ";
gets(str1);
len = strlen(str1) - 1;
for (i = len, j = 0; i >= 0 ; i--, j++)
str2[j] = str1[i];
if (strcmp(str1, str2))
flag = 1;
if (flag == 1)
cout << str1 << " is not a palindrome";
else
cout << str1 << " is a palindrome";
return 0;
}
It will work in every case you can try.

Answer 2

If you get a mismatch i.e. (characters[m] == characters[n]) is false then you do not have a palindrome. You can break the loop at that point, returning false as your result. You do not do that, instead you carry on testing when the result is already known. I would do something like:
// Check the characters.
int lo = 0;
int hi = char_length - 1;
int result = true; // Prefer "true" to 1 for better readability.
while (lo < hi) { // Loop terminates when lo and hi meet or cross.
if(characters[lo] != characters[hi]) {
// Mismatched characters so not a palindrome.
result = false;
break;
}
lo++;
hi--;
}
I have made a few stylistic improvements as well as cleaning up the logic. You were doing too much work to solve the problem.
As an aside, you do not need to check when the two pointers lo and hi are equal, because then they are both pointing to the middle character of a word with an odd number of letters. Since that character must be equal to itself there is not need to test. Hence the < in the loop condition rather than <=.

Answer 3

Existing Code does not work for Palindromes of Odd Length because of
for(int i = 0; i < sizeof(booleans)/sizeof(booleans[0])-1; i++)
Either use i<=sizeof(booleans)/sizeof(booleans[0])-1; or i<sizeof(booleans)/sizeof(booleans[0]);.
Currently, you are not counting the comparison of character[middle-1] and character[middle+1].
For palindromes of even length, you will have to change your logic a bit because even length palindromes don't have a defined middle point.
#include <iostream>
#include <cstring>
using namespace std;
int main(){
//take input
string input;
cout << "Enter your word: ";
cin >> input;
//initialize arrays and variables
int counter = 0, k = 0;
int char_length = input.length();
char characters[char_length];
strcpy(characters, input.c_str());//copy the string into char array
//index of character at the midpoint of the character array
int middle = (char_length+1)/2;
int booleans[middle]; //to keep 1's and 0's
//check the characters
int m = 0, n = char_length-1;
while(m<=n){
if(characters[m] == characters[n]){
booleans[k] = 1;
} else {
booleans[k] = 0;
}
k++;
m++;
n--;
}
//count number of 1's (true for being equal) in the booleans array
for(int i = 0; i < sizeof(booleans)/sizeof(booleans[0]); i++){
counter += booleans[i];
}
cout<<counter<<" "<<middle<<endl;
//compare 1's with size of array
if(counter == middle){
cout << input << " is a Palindrome!" << endl;
} else {
cout << input << " is not a Palindrome!" << endl;
}
return 0;
}
Over here the size of the boolean array is (length+1)/2,
For string s like abcba it will be of length 3.
This corresponds to a comparison between a a, b b and c c. Since the middle element is the same, the condition is always true for that case.
Moreover, the concept of middle is removed and the pointers are asked to move until they cross each other.