In C, my code to find the palindrome is either not printing out all the chars, missing a single char, or repeating chars?

Question

I am working on homework and my assignment is to find the palindrome in the string. My code is not printing out all the chars or missing a char, or repeatedly printing chars. I tried to post as many details as possible on my code. I hope someone can help me through this code. *I have posted this question before but this question has new updated code which is very different from what I had before.

#include <stdio.h>
#include <string.h> 
int palindromelength(char *str, int i, int j);
char str[100];  
int main()
{
    int i,j,len,n;
    printf("Enter a string ");      
    fgets(str,sizeof(str),stdin);//takes user input
    str[strcspn(str, "\n")] = 0;
    len=strlen(str);
    palindromelength(str, 0, len-1);//function call
    return 0;       
}
int palindromelength(char *str, int i, int j) 
{       
    int len=strlen(str),n;
    printf("length is %d\n", len);
    while(i<len-1)
    {       
    printf("i=%d\n",i);
        for(j=len-1;j>=(len/2)-1 ;j--)
        {           
            printf("%c%c\n",str[i],str[j]);           
            if(str[i]==str[j])//if letters aren't same
            {
               printf("if: i=%d j=%d str[%d]=%c str[%d]=%c\n",i,j,i,str[i],j,str[j]);
            // printf("%c%c",str[i]);/***in my final code I will print this statement 
           //and all the other printfs will be removed. So there won't be new line.***/
            }                               
        }
        i++;    
    }
    return 0;   
}

***only str[i] will be printed in final code***
Output:        expected:abcba
Enter a string abcbae
length is 6
i=0
ae
aa
if: i=0 j=4 str[0]=a str[4]=a
ab
ac
i=1
be
ba
bb
if: i=1 j=3 str[1]=b str[3]=b
bc
i=2
ce
ca
cb
cc
if: i=2 j=2 str[2]=c str[2]=c
i=3
be
ba
bb
if: i=3 j=3 str[3]=b str[3]=b
bc
i=4
ae
aa
if: i=4 j=4 str[4]=a str[4]=a
ab
ac

output 2:                       expected:aba 
Enter a string dabae
length is 5
i=0
de
da
db
da
i=1
ae
aa
if: i=1 j=3 str[1]=a str[3]=a
ab
aa
if: i=1 j=1 str[1]=a str[1]=a
i=2
be
ba
bb
if: i=2 j=2 str[2]=b str[2]=b
ba
i=3
ae
aa
if: i=3 j=3 str[3]=a str[3]=a
ab
aa
if: i=3 j=1 str[3]=a str[1]=a

output 3:                    expected:racecar
Enter a string racecar
length is 7
i=0
rr
if: i=0 j=6 str[0]=r str[6]=r
ra
rc
re
rc
i=1
ar
aa
if: i=1 j=5 str[1]=a str[5]=a
ac
ae
ac
i=2
cr
ca
cc
if: i=2 j=4 str[2]=c str[4]=c
ce
cc
if: i=2 j=2 str[2]=c str[2]=c
i=3
er
ea
ec
ee
if: i=3 j=3 str[3]=e str[3]=e
ec
i=4
cr
ca
cc
if: i=4 j=4 str[4]=c str[4]=c
ce
cc
if: i=4 j=2 str[4]=c str[2]=c
i=5
ar
aa
if: i=5 j=5 str[5]=a str[5]=a
ac
ae
ac

Answer 1

Your code is doing exactly what you've asked of it.

You're scanning through the string and then scanning backwards from the other end to find any matching characters and not yet checking for palindromes. The reason why your code is giving you odd results when doing this is because of the inner loop.

for(j=len-1;j>=(len/2)-1 ;j--)

You stop j from going beyond the middle of the string, but allow i to traverse all of it. This means that you get points where i is more than j like in this example bit of output:

if: i=4 j=2 str[4]=c str[2]=c

Or sometimes the matching end character could be before the middle of the string.

You want to constrain j so that it is always more than i like so...

for(j=len-1;j>i ;j--)

...or maybe make it j>=i if you're happy to match the same character with itself.

Answer 2

You made a simple program into complex code. As far as i understand you need to check whether the input string is palindrome or not.Here is the simple sample code for that in c

#include <stdio.h>

int main()
{
   char s[1000], r[1000];
   int begin, end, count = 0;

   printf("Input a string\n");
   fgets(s,sizeof(s),stdin);

   // Calculating string length

   while (s[count] != '\0')
      count++;

   end = count - 1;

   for (begin = 0; begin < count; begin++) {
      r[begin] = s[end];
      end--;
   }

   r[begin] = '\0';

   printf("%s\n", r);
 if(strcmp(s,r)==0)
{
printf("panlindrome");
}
else
{
printf("not palindrome");
}
   return 0;
}