logical operator problem.

Xiangbuilder · 09-06-2003, 11:34 PM

Does the line:

Code:

if (c == ' ' || c == '\n' || c = '\t')

right?

Here is the source code I copy from <<the c programming language>>

Code:

     #include <stdio.h>

   #define IN   1  /* inside a word */
   #define OUT  0  /* outside a word */

   /* count lines, words, and characters in input */
   main()
   {
       int c, nl, nw, nc, state;

       state = OUT;
       nl = nw = nc = 0;
       while ((c = getchar()) != EOF) {
           ++nc;
           if (c == '\n')
               ++nl;
           if (c == ' ' || c == '\n' || c = '\t')
               state = OUT;
           else if (state == OUT) {
               state = IN;
               ++nw;
           }
       }
       printf("%d %d %d\n", nl, nw, nc);
   }

however, when I compile it, the compiler said:
"[root@localhost second]# gcc c.c -o c
c.c: In function `main':
c.c:17: invalid lvalue in assignment"

What is wrong with the program?
Thank you.

Mohsen · 09-07-2003, 12:05 AM

Sure it should be (... c == '\t' )
because it wants to ignore white spaces.
Also in my book (second edition), it's corrected.

Xiangbuilder · 09-07-2003, 12:31 AM

Sorry for my simple question.
Now I know it is a publishing mistake.

eric.r.turner · 09-07-2003, 11:34 AM

You're fortunate that you have a compiler that would even warn you about this. Many C compilers wouldn't! This is such a common mistake that many programmers recommend doing:

Code:

if( '\t' == c )

instead of

Code:

if(c == '\t')

so that you guarantee that the compiler will catch the "= instead of ==" mistake. I personally don't follow that advice because it's never been a problem for me, but you can see that even authors of C books can make the mistake! What page is that mistake on? My book is at work, so I can't look it up. I'm surprised that K&R published that mistake!

Hko · 09-07-2003, 03:13 PM

Quote:

Originally posted by eric.r.turner
What page is that mistake on? My book is at work, so I can't look it up. I'm surprised that K&R published that mistake!

In the second edition the mistake is not there, but the program is.
In the second edition it's on page 20, chapter 1, section 1.5 ("Character input and output").

Xiangbuilder · 09-07-2003, 10:02 PM

Thank you teach me many things.
I downloaded the book from web and pay nothing for it.
In other words, my action is a kind of software crime.
Perhaps that is why the publishing mistake occur.
My English is poor, perhaps I don't explain my meaning exactly.