program to know all the huiwen number doesn't work well - c

Question

this program is build to know all the huiwen number from 1 to 256
like 11^2=121 so 11 is a huiwen.
actually I have a good one
but I am confuse about why this program doesn't work well.
#include<stdio.h>
int is_huiwen(int l)
{
//DON'T WORK?WHY?
int number[20]={0};
int i,j,k;
int f=l*l;
for(j=0;f;j++)
{
number[j]=f%10;
f/=10;
}
for(k=0;j-k>0;k++,j--)
{
if(number[j]!=number[k] )
{
return 0;
}
}
return 1;
/* this is ok
int y=0;
int t = l*l;
int x = t;
do
{
y=y*10+t%10;
t /= 10;
}
while(t);
if(x==y)
return 1;
else
return 0;
*/
}
int main()
{
int i;
int flag;
for(i=0;i<256;i++)
{
flag=is_huiwen(i);
if(flag)
{
printf("%d is huiwen",i);
}
else
{
printf("\n");
}
}
printf("end\n\n\n\n");
return 0;
}
end.

Answer 1

The error is the if( number[j] != number[k] )line as pointed out by BluePixy.
The correction is if( number[j-1] != number[k] )
I would to point out that the code has hidden the problem partly because of a smattering of one letter variable names and inconsistent naming.
Here is the code that I used to find the same solution
int is_huiwen_2(int L )
{
int ret = 1;
int j = 0;
int k = 0;
int t = L * L;
int number[8] = { 0 };
for( j = 0; t; j++)
{
number[j] = t % 10;
t /= 10;
}
for( k = 0; (j - k) > 0 && ret; k++, j-- )
{
if( number[j-1] != number[k] )
{
ret = 0;
}
}
return( ret );
}
int is_huiwen_1( int L )
{
int ret = 1;
int y = 0;
int t = L * L;
int x = t;
do
{
y = y * 10 + t % 10;
t /= 10;
}
while( t );
if( x != y )
{
ret = 0;
}
return( ret );
}
int main()
{
int i = 0;
int flag = 0;
for( i = 0; i < 256; i++)
{
flag = is_huiwen_1(i);
if(flag)
{
printf("1: %d is huiwen\n",i);
}
}
for( i = 0; i < 256; i++)
{
flag = is_huiwen_2(i);
if(flag)
{
printf("2: %d is huiwen\n",i);
}
}
printf("end\n");
return( 0 );
}
I don't know what all the variables do. The use of 'l' looks like a '1' in some editors.
Being a Code Refactoring monk or zealot, I did some modifications such as reducing the code to one consistent return condition, value and point of return.
While it might seem overly simple, having multiple declarations on one line hides trouble, such as int i not being used in the second function.
The use of int numbers[20] = { 0 }; was also misleading us as for the range of values here [20] was overkill, having an explanation of what the range of values "12321", "1234321" where could have meant easier debugging of this code. A simple comment of what the outcome should look like would have solved several problems.
// A Huiwen number looks like this "12321", "1589851"
While this might be a simple exercise it portends greater problems down the line if this was not a trivial exercise. Try not to make it hard on the next coder.
Document your algorithms, arithmetic and variables please.