K & R section 1.10 example program skipping 'printf()' line - c

Question

I'm learning C through K & R. I have reached to section 1.10 External Variables and Scope.
In that section they have written and explained program regarding external variable and their scope. I typed that code myself and tried to execute it. It does not show any run time or compile time error. However, it does not print any output also, which should be longest line from given input. I did debug the program and I found that program is skipping 'printf()' statement. I tried both on sublime text 2 + gcc and Turbo c++ v4.5, but still I don't get an output. I'm using Windows xpsp 3.
Here is my code :
#include<stdio.h>
/* program to pring longest line using external variables */
#define MAXSIZE 1000
int max;
char line[ MAXSIZE ];
char longest[ MAXSIZE ];
int getline( void );
void copy( void );
main()
{
int len;
extern int max;
extern char longest[];
max = 0;
while( ( len = getline() ) > 0 )
{
if( len > max )
{
len = max;
copy();
}
}
if( max > 0)
printf("\n%s\n", longest); /* This line is skipped */
return 0;
}
int getline( void ) /* Check if there is line */
{
int c, i;
extern char line[];
for( i = 0; i < MAXSIZE -1 && ( c = getchar()) != EOF && c != '\n'; ++i )
line[ i ] = c;
if( c == '\n' )
{
line[ i ] = c;
++i;
}
line[ i ] = '\0';
return i;
}
void copy( void ) /* copy current line to longest if it is long */
{
int i = 0;
extern char line[];
extern char longest[];
while( ( longest[ i ] = line[ i ] ) != '\0' )
++i;
}
So my questions are :
Why is this happening?
What should I do so that program won't skip 'printf()' and will print an output?
Please help. Thank you.

Answer 1

The intent of this code is to start max at zero then, for every line longer than the current max, copy the line and update max to the longer value:
max = 0;
while( ( len = getline() ) > 0 )
{
if( len > max )
{
len = max;
copy();
}
}
However, the line that's supposed to update max is assigning in the wrong direction. It sets len to be the current value of max and never updates max at all. This is something that would have been obvious with a bit of "Debugging 101", placing the following line after the call to copy():
printf ("New long line, len = %d, str = '%s'\n", max, longest);
That fact that you would never have seen the length changing would have (hopefully) narrowed down the problem pretty fast. The line in question should instead be:
max = len;