a program for palindrome in C

[shahzaib1111]

well i have created a program but my logic is little bad ,,
can any one help to improve my logic a little please
(i cant understand c++,, i am beginner to C )

#include<conio.h>
#include<stdio.h>
int i=0,j=0,k=0,a;
void main ()
{
char arr[200];

while ( (arr[i]=getche()) != '\r')
{
		i++;
		a++;
}
for (i=0;i<=(a/2);i++)                         /*logic of this two loops are , we will take one loop from start to half hand other from end to half, then compare both*/ 
{											   /*these two loops will repeat equally*/
	for(j=(a-1);j>=a/2;j++)
	{
		if (arr[i]==arr[j])
		{
			
				printf("this string is pelindrome");
			
		}
	}
}
getch()

[andywestken]

Hi

Could you edit your orig. post to sort out the formatting. In particular the indenting (of scopes). It's quite hard to read at the mo'.

But from what I can see through the "murk"...

#1 a is not inititlized (to 0), so it's been incremented from an unknown value.

suggestion: use single declaration per line to make this clearer

#2 main should return int (a void return is non-standard)

#3 you only need one loop. replace your two by a single one

these two loops will repeat equally

Not true! To start with, the second loop is incrementing when it should be decrementing!

But when j-- is used instead of j++, it is still not right as the j loop is nested inside the i loop. If you log the comparisons made, you will see it tries (for "hello")

i = 0, j = 4
i = 0, j = 3
i = 0, j = 2
i = 1, j = 4
i = 1, j = 3
i = 1, j = 2
i = 2, j = 4
i = 2, j = 3
i = 2, j = 2

which is not what you need here!

#4 the point you say it's palindrome is not right: you only know it it is one at the end of the loop(s)

#5 your input code looks unnecessarily complicated. see
http://www.cplusplus.com/reference/clibrary/cstdio/gets/

And while I was at it, I'd give some of you variables better names!

Andy

[vlad from moscow]

getche is not a standard C function. So it is better if you will not use it.
Also your code is invalid. You should use a single loop to compare two parts of the character array.