Test Palindrome

HI,

My goal is to write a program to test if a particular string is a palindrome (string that's spelled the same way backwards and forwards ). Here is the code but it doesn't work, it always return false, i don'tk now why, pls tell me whats wrong, thnx in advance!

Code:

---

/* Palindrome */

#include <stdio.h>

int testPalindrome( char array[] );

int main()
{
  char string[ 6 ] = "ellle";

  if ( testPalindrome( string ) == 1 )
      printf( "String is a palindrome.\n " );
  else if ( testPalindrome( string ) == 0 )
      printf( "String is not a palindrome.\n" );

  getch();

  return 0;
}

int testPalindrome( char array[] )
{
  int length = 0;
  int i = 0;

  i = 0;

  while ( array[ i ] != '\0' ) {
      ++length;
      i++;
  }

  if ( length - 1 == 0 || length - 1 == 1 )
      return 1;
  else if ( array[ 0 ] != array[ length - 2 ] )
      return 0;
  else {
      array[ 0 ] = '\0';
      array[ length - 2 ] = '\0';
      for ( i = 0; i < 6; i++ )
        printf( "%c", array[ i ] );

      return testPalindrome( array );
  }
}

---

You could write it

Code:

---

int palindrome(char* s)
{
    return palindrome_recur(s, 0, strlen(s)-1);
}

int palindrome_recur(char* s, size_t low, size_t high)
{
    if (low >= high)
            return 1;
 
    return s[low] == s[high] && palindrome_recur(s, low+1, high-1);
}

---

is there a way of doin it without using pointers ?

use strrev() to reverse the string and then test with strcmp() to see if the reversed string matches the original.

Should be about three lines.

EDIT
When I looked up strrev() in MSDN it has the code to do test for palindromes.

Code:

---

void main( void )
{
  char string[100];
  int result;

  printf( "Input a string and I will tell you if it is a palindrome:\n" );
  gets( string );

  /* Reverse string and compare (ignore case): */
  result = _stricmp( string, _strrev( _strdup( string ) ) );
  if( result == 0 )
      printf( "The string \"%s\" is a palindrome\n\n", string );
  else
      printf( "The string \"%s\" is not a palindrome\n\n", string );
}

---

the thing is, i am doin a exercise, which i can only use normal coding techniques. I can't use pointers coz i haven't learnt that yet and can't use any other functions except the stdio.h and the functoins that i wrote.

thnx

OK, should have realised, no one needs to find palindromes on their own.
Need a pointer to send the string into the function as an array and sending in the first element of the array (eg szBuffer[0]).
Could do it all in the main function or make the string global to avoid passing the pointer.

Code:

---

int FindPalindrome(char  *szBuffer)
{
int    iStart=0,iEnd=0;

while(szBuffer[iEnd] != '\0')
    iEnd++;
//back off one so szBuffer[iEnd] is not = '\0'
iEnd--;
while(iStart<iEnd)
{
    if(iStart==iEnd)//meet in the middle
        return TRUE;
    if( (szBuffer[iStart]) == (szBuffer[iEnd]) )
    {
        iStart++;
        iEnd--;
    }
    else return FALSE;//not matched so not a palindrome
}
return TRUE;
}

---

call this with


if( FindPalindrome(szStringToTest) )
{
// is palindrome
}
else //is not

do u mean that it's not possible to do it recursively without the use of pointers ?

BTW your code worked beautifully thnx

It's possible, just replace
int FindPalindrome(char *szBuffer)
with
int FindPalindrome(char szBuffer[])

When you use array notation to pass a string to a function the compiler will turn it into a pointer, so both of the above calls will do the same thing.