K&R book example for »getchar()« program stumps me

I must say that I'm just starting with C Programming. I've had the urge to do so and decided to. Prior to this however, I was a complete BASIC programmer, which makes it a little hard for me to understand some things.

K&R's »The C Progamming Language« is the book that I have decided to use (I've tried Bruce Eckel's »Thinking In C« before, but nevertheless thought this might clear some problems)

Chapter 1.5.4 »Counting Words« has a program that I found hard to understand:

Code:

---

#define IN 1
#define OUT 0

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);
}

---

I cannot understand how this works. How does the while loop allow the number of words to be counted? I don't see c having any index operations on it.

Bashing is accepted humbly :D

Thank you!

Well have you figured out that nl = number of lines, nw = number of words and nc = number of characters.

Yes, I was expecting an answer like this. But how are these variables supposed to help. Shouldn't there be an index or something to tell the position of the letter in order to Move forward?

Quote:

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Originally Posted by ChipOManiac

Yes, I was expecting an answer like this. But how are these variables supposed to help. Shouldn't there be an index or something to tell the position of the letter in order to Move forward?

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There is no position, getchar just reads input from the keyboard, which is a stream. To count words, you only need to know when you cross a boundary, from non-word (state == OUT) to word (state == IN). Note that this program considers space, newline and tab "non-word" characters, everything else would be considered a "word" character.

Quote:

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Originally Posted by ChipOManiac

Bashing is accepted humbly :D

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BASIC?!?!?

Quote:

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Originally Posted by Edgser W Dijkstra

It is practically impossible to teach good programming to students that have had a prior exposure to BASIC: as potential programmers they are mentally mutilated beyond hope of regeneration.

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;) :p

Do you understand what happens when you use this code?

Code:

---

while ((c = getchar()) != EOF)
{
...
}

---

Spend a day or two until you have a real understanding of this and you will be able to finish the chapter much easier. Once you do, you will know what the exercises are about and what the implementation need to look like to be any good.

Quote:

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Originally Posted by anduril462

There is no position, getchar just reads input from the keyboard, which is a stream. To count words, you only need to know when you cross a boundary, from non-word (state == OUT) to word (state == IN). Note that this program considers space, newline and tab "non-word" characters, everything else would be considered a "word" character.

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Does that mean that at every while loop the whole string is sent character by character to the body?

Quote:

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Originally Posted by anduril462

BASIC?!?!? ;) :p

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Oh shucks! :( I knew I should have started with C :( Am I really doomed though?

Quote:

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Originally Posted by Newbi2C

Do you understand what happens when you use this code?

Code:

---

while ((c = getchar()) != EOF)
{
...
}

---

Spend a day or two until you have a real understanding of this and you will be able to finish the chapter much easier. Once you do, you will know what the exercises are about and what the implementation need to look like to be any good.

---

Thank you! apparently this is probably all I need.

Quote:

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Originally Posted by ChipOManiac

Thank you! apparently this is probably all I need.

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If you understand what the loop does, you will have no problem interpreting the conditional expressions used for the program. What the program does is basically to take characters and place them in c until the EOF (end of file) is reached if the character is a space, tab or newline (return) it goes into a new state where it is looking for a character that is not a space, tab or newline. When/if it run into one; it add 1 to nw (new word).

Since the state machine is the same in both BASIC and C I assumed you had some problem understanding what the while-loop did. I think Q-BASIC (which is the first BASIC I tried) has the same code once within the IF-conditional(?*)

*English is not my 1:st language...

Quote:

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Originally Posted by Newbi2C

Since the state machine is the same in both BASIC and C I assumed you had some problem understanding what the while-loop did. I think Q-BASIC (which is the first BASIC I tried) has the same code once within the IF-conditional(?*)

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I was under the assumption that the while loop was waiting for an EOF to break the process of line-by-line input, not that it was using getchar() to feed each character from the stream.

I thought that, since I had used fgets previously and that getchar seemed to just push out a string that, getchar was just the same as fgets. Which brought me to the »index« issue (gosh I'm ignorant)

There's no excuse for it, I apologize.

However thanks for »not fishing for me« :)

Thanks to the others as well.

Since you are working through K&R, you may find some value in Steve Summit's Notes to Accompany K&R

Quote:

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Originally Posted by AndrewHunter

Since you are working through K&R, you may find some value in Steve Summit's Notes to Accompany K&R

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Thank you!