C++ Palindrome Bool Function (Using Pointer)

Question

How to create a Palindrome function in C++? I'm using 2 functions types(bool and void). Here is my code so far (I would really appreciate any help with this, and why my code is not working?) Thank you!

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


void reverse(char *);  
bool isPalindrome(char *);  

int main()  
{  
    char a[10];  
    cout << "string ";  
    cin.getline(a, 10);  
    if (palindrome(a))  
        cout << "true";   
    else  
        cout << "false";  
    return 0;  
}  
void reverse(char *s)  
{  
    char *point = s;  
    int i, min;  
    for (i = 0; *point != '\0'; i++)  
        point++;  
        min = i;  
        point--;  
    for (i = min; i > 0; i--)  
   {  
        cout << *point--;  
   }  
}  
bool ispalindrome(char *s)  
{  
    bool status;  
    char *original = s;  
    char *point = s;  
    reverse(point);        
    for (int i = 0; point != '\0'; i++)  
    {  
        if (point[i] == original[i])  
        status = true;  
        else  
        status = false;  
    }  
    return status;  
}

Answer 1

you dont need to reverse the string to check if its palindrome.

the algorithm works like:

get the length of the string;
loop from zero to length of string by 2;
compare the characters on position loop count with lenght minus loop count minus 1;
if the are not equal its not a palindrom;
its a palindrome if the loop finished;

for example: "test":
first step: compare 't' with 't'
second step: compare 'e' with 's' --> not a palindrom

for example "palap":
first step: compare 'p' with 'p'
second step: compare 'a' with 'a'
third step: compare 'l' with 'l'
now we know that it is a palindrom.

try thisone:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int palindrom(char * s){
  int i;
  int l = strlen(s);
  for(i=0;i<=l/2;i++)
    if(s[i]!=s[l-i-1]) return 0;
  return 1;
}

int main(void) {
  char * test = "test";
  char * pal = "palap";
  printf("%s %d", test, palindrom(test));
  printf("%s %d", pal, palindrom(pal));
  return 0; 
}

Answer 2

Several things that can be improved here. Your most immediate problem is that the for loop in your isPalindrome function doesn't terminate. Change the terminating condition to point[i] != '\0'.

Secondly the reverse function is not actually reversing. if you want to use this algorithm you'll need to allocate memory for the reversed string. A better way though is to put a pointer at the front of the string, a pointer at the end of the string, and then walk them to the middle of the string.

Answer 3

Similar to the answer from @linluk using pointers instead of indices...

#include <cstring>
bool palindrome(char *s)  
{
    for (char *e = strchr(s, '\0'); -- e > s; ++ s)
        if (*e != *s)
            return false;
    return true;
}

Initially, e, points to the end of the string and s points to the beginning. In each iteration, e steps backward while s steps forward until they meet in the middle. If, they ever point to a different character from one another, the test fails.