Checking for a palindrome

Question

The following code is supposed to check for palindromes of up to nine characters, though I set the array to ten to leave space for the null. The problem is when the command screen comes up to enter the information, is freezes every time. I am not sure where the problem lies, and am also sure that there are errors in the code that I haven't been able to notice. Any help is appreciated.

#include <stdio.h>
#include <stdlib.h>
/*Delare the prototypes*/
char palindromes(char[], int, int);
char backwards(char[], int, int);

int main ()
{
   const int arraysize= 10;/*Sets a size for the array*/
   char userinput[10];/*Declares the character array for the input*/
   int palindex= 0;/*Declares the index to check for a palindrome*/
   int index= 0;/*Index for the counting loop*/
   int counter= 0;/*Counts number of elements entered in the array*/
   int palcheck= 1;/*Sets a value for the palindrome checking loop, for verification*/
   int charswap= 0;/*Sets an index for the loop that swaps the values*/
   int printindex= 0;/*Index to print the values on the screen*/

   printf("Please enter a series of nine or less characters to test for a palindrome.\n");
   scanf(" %9s", &userinput);
   printf("\n");

   for(index; userinput[index] !=0; index++)
   {
      counter +=1;
   }/*End of array element counter*/


   for(palindex; palindex < (counter/2); palindex++)
   {
      palcheck= palindromes(userinput, counter, palindex);
      if(palcheck = 0)
      break;
   }/*End of palidrome verification loop*/

   if(palcheck = 0)
   {
      printf("Your input was not a palindrome \n");
   }/*End of if statement*/
   else
   {
      printf("Your input was a palindrome \n");
   }/*End of else statement*/

   for(palindex; palindex < (counter/2); palindex++)
   {
      backwards(userinput, counter, palindex);
   }/*End of reversing the array loop*/

   printf("Your input backwards is: ");
   for(printindex; printindex < counter; printindex++)
   {
      printf("%c", userinput[printindex]);
   }/*End of printing backwards loop*/
}/*End of main function*/

char palindromes(char userinput[], int counter, int palindex)
{
   char firstchar;/*Temp variable for the two items to be tested*/
   char lastchar;/*Temp variable for the two iteams to be tested*/
   firstchar = userinput[palindex];
   lastchar = userinput[counter - palindex];
   if(firstchar = lastchar)
   {
      return 1;
   }
   else
   {
      return 0;
   }
}/*End of palidrome function*/

char backwards(char userinput[], int counter, int palindex)
{
   char temp;/*Sets a temporary value to swap the two values*/
   temp = userinput[palindex];
   userinput[palindex] = userinput[counter-palindex];
   userinput[counter-palindex] = temp;
}/*End of reverse function*/

Answer 1

There were too many things wrong to really remember, just go line by line, but here are some starters

• in all of your if statements you're overwriting your variables, use == instead of =
• your counter is doing nothing, use scanf with %n to find the number of read characters
• you don't want to pass in the counter variable to your palindromes function as the middle argument because of the trailing '\0' in your input string... instead use counter-1

there might have been others, but here's a minimally working version of your original code:

#include <stdio.h>
#include <stdlib.h>
/*Delare the prototypes*/
char palindromes(char[], int, int);
char backwards(char[], int, int);

int main ()
{
   char userinput[10];/*Declares the character array for the input*/
   int palindex= 0;/*Declares the index to check for a palindrome*/
   int index= 0;/*Index for the counting loop*/
   int counter= 0;/*Counts number of elements entered in the array*/
   int palcheck= 1;/*Sets a value for the palindrome checking loop, for verification*/
   int charswap= 0;/*Sets an index for the loop that swaps the values*/
   int printindex= 0;/*Index to print the values on the screen*/

   printf("Please enter a series of nine or less characters to test for a palindrome.\n");
   scanf(" %9s%n", &userinput, &counter);
   printf("\n");
   for(palindex; palindex < (counter/2); palindex++)
   {
      palcheck = palindromes(userinput, counter-1, palindex);
      if(palcheck == 0)
      break;
   }/*End of palidrome verification loop*/

   if(palcheck == 0)
   {
      printf("Your input was not a palindrome \n");
   }/*End of if statement*/
   else
   {
      printf("Your input was a palindrome \n");
   }/*End of else statement*/

   for(palindex; palindex < (counter/2); palindex++)
   {
      backwards(userinput, counter, palindex);
   }/*End of reversing the array loop*/

   printf("Your input backwards is: ");
   for(printindex; printindex < counter; printindex++)
   {
      printf("%c", userinput[printindex]);
   }/*End of printing backwards loop*/
   printf("\n");
}/*End of main function*/

char palindromes(char userinput[], int counter, int palindex)
{
   char firstchar;/*Temp variable for the two items to be tested*/
   char lastchar;/*Temp variable for the two iteams to be tested*/
   firstchar = userinput[palindex];
   lastchar = userinput[counter - palindex];
   if(firstchar == lastchar)
   {
      return 1;
   }
   else
   {
      return 0;
   }
}/*End of palidrome function*/

char backwards(char userinput[], int counter, int palindex)
{
   char temp;/*Sets a temporary value to swap the two values*/
   temp = userinput[palindex];
   userinput[palindex] = userinput[counter-palindex];
   userinput[counter-palindex] = temp;
}/*End of reverse function*/