Need Help - The C Programming Language 2nd ed K&R Book

[kgc210]

I just bought the book and I have started to read through it.

For the time being I am using vbcc on WINUAE but it's setup the same as my 90mhz 060 A4000 (BetterWB).

I will start compiling on my A4000 shortly but I am really scratching my head so soon into this book.

I did the temp conversions really ok reversing the Fahrenheit to Celsius code ok and adding in headers to describe what the columns were. I thought I was an 31337 hacker hahaha

I am now on section 1.5.1 File Copying
I understand the concept that what I type into the shell is displayed. But I cant get my head around exercises:

Exercise 1-6. Verify that the expression getchar () I= EOF is 0 or 1.
Exercise 1-7. Write a program to print the value of EOF.

The given code is:

#include <stdio.h>

main()

{

    int c;

    while ((c = getchar()) != EOF)

        putchar(c);

}

I have had a google and I am not the only one confused, there is a post on Stackoverflow but that didn't help much either
I know I must trigger an EOF but don't know how and would it display EOF or just exit the program?

Thanks in advance for any help given.

[alkis]

Ok, let's start with the keyboard. "Ctrl \" I think is what sends EOF in Amiga Shell. "Ctrl d" is on linux. So the key sequence varies from OS to OS.

But you can redirect input from a file. Say you have a file foo.txt (make one, write a sentence in it and save it). Say your executable is called filecopy. Then you can do

filecopy <foo.txt

That will read the foo.txt and when the last byte has been read then the next call in getchar() will return EOF.

Now, onto your last question. The snippet you posted will just exit when EOF is seen.

EOF is really an integer. If you want to print it's value, try this:
printf("EOF's value is %d\n", EOF);

[kgc210]

Thanks for the help.
I couldn't get filecopy to work kept getting: unknown identifier <filecopy>

I wasn't far off printing EOF then I was missing the "%d" part.

I noticed a few odd things when you type in special characters.
If i typed in say "@blablabla" and pressed Return (minus the quotes)
It would display:
@blablabla
@blablabla
and the cursor would be hear. @ seems to repeat everything on a line.

If I did "Ctrl 2" I would get an inverted @ and when pressing Return the cursor would drop down two lines.

If I try "Ctrl 2" on my PC I either switch tab on a browser and If I try to do it in say notepad nothing is displayed.

[phx]

Originally Posted by kgc210

I couldn't get filecopy to work kept getting: unknown identifier <filecopy>

This was just an example. Alkis thought you would call your excercise program "filecopy". Replace "filecopy" with the actual program name.

If i typed in say "@blablabla" and pressed Return (minus the quotes)
It would display:
@blablabla
@blablabla
and the cursor would be hear. @ seems to repeat everything on a line.

No. I doubt that. And I bet it also works with other characters.

You have to know that getchar() reads characters from the file stdin, and stdin is usually the console, as long as you don't redirect it with "<" (see above).

The console is not a normal file, like a file on disk. It is an interactive TTY, which is line-buffered. So your getchar() call is blocked until another line-buffer is complete, which happens after you pressed the Return key. Then it returns all typed characters from that line, one after another, until the '\n' Character (decimal 10 = Newline). Then it blocks again, waiting for the next line-buffer.

From the two lines you are seeing the first line is the echo of your typed characters in the shell (your program is still blocked in the first getchar() call). The second line is actually generated by your program with getchar()/putchar().

If I did "Ctrl 2" I would get an inverted @ and when pressing Return the cursor would drop down two lines.

This depends on the system and the shell being used. On a standard AmigaOS 3.1 shell I don't see that.

[kgc210]

I am sorry but I can't figure out how to get getchar() to read <foo.txt

I have tried it in the brackets out side them. Deleted the whole lot and just had <foo.txt

Not sure if to carry on reading this book or look for a more simple "Retards guide to C" book

[Locutus]

the stdin redirection suggestion is more a native unix thing, i'm not sure it actually works on AmigaOS' shell.

[alkis]

Originally Posted by Locutus

the stdin redirection suggestion is more a native unix thing, i'm not sure it actually works on AmigaOS' shell.

I am sure

[alkis]

Originally Posted by kgc210

I am sorry but I can't figure out how to get getchar() to read <foo.txt

I have tried it in the brackets out side them. Deleted the whole lot and just had <foo.txt

Not sure if to carry on reading this book or look for a more simple "Retards guide to C" book

what's the name of your executable that is produced after you compile the example source code?

[kgc210]

Right I get it now, I have to type the <foo.txt into the shell.

I thought I was trying to get "getchar()" to read it with in the program it's self.

[kgc210]

Well I'm onto Exercise 1-8

Write a program to count blanks, tabs and newlines.

I had a look at an ASCII table and found I needed to add \s and \t to my code.

When I tried \s (also tried escape \e) I get the error "illegal escape-sequence in string" when trying to compile the code.

Is this due to vbcc blocking \s or something Amiga specific?

Anyway I changed \s to backspace \\ and got it to compile.

#include <stdio.h>



main ()

{

int c, nl, tb, bs;



nl = 0;

tb = 0;

bs = 0;



while ((c = getchar()) != EOF)

if (c == '\n')

++nl;

if (c == '\t')

++tb;

if (c == '\\')

++bs;



printf("%d\t%d\t%d\n", nl, tb, bs);

}

It counts newlines ok but if I press tab or backspace it doesn't record them.
I also created a txt file with ed to have some new lines and tabs in, but again it didn't see them.
I also tried to write \\, \t in the txt file.

Is this due to the way Amiga handles tab and backspace? Or because ed can't encode them in a file?

On the attached image you can see where I tried to press Tab in the shell, it displayed inverted I

Thanks Will

[alkis]

Ok, lets break it down.

Write a program to count blanks, tabs and newlines.

blanks are space " "
tabs are \t
newlines are \n

Backspace is not blank, so you should not count it. Even if you needed to count backspace you couldn't, because backspace doesn't leave a char behind, it just erases a char left from cursor.

Also, the '\\' is not backspace is the char '\' (backslash)

The backspace is '\b', which again you'll never be able to get. (Technicaly you could if you put the console in raw mode, but that's way advanced for this exercise)

Bottom line, if you changed the
if (c == '\\')
to
if (c == ' ')

then I think you'll cover what the exercise asked you to do.

Emm, just saw the screenshot. You forgot the braces in your while. Enclose all ifs in {} like

while(...) {
   if...
   if...
   if...
}

[phx]

Originally Posted by kgc210

When I tried \s (also tried escape \e) I get the error "illegal escape-sequence in string" when trying to compile the code.

Is this due to vbcc blocking \s or something Amiga specific?

\s is no legal ANSI-C or ISO-C escape code. Here is an overview of all the legal ones:
https://en.wikipedia.org/wiki/Escape_sequences_in_C

[kgc210]

Thanks alkis and phx I owe you both a beer.

I have just rebuilt my WINUAE setup on the laptop, I forgot to copy the hard file before going on my travels to Rheda-Wiedenbruk

I will give the coding a go tomorrow evening when I arrive, I have the C book in the car.

I will keep you both posted.

Do you think all this ASCII stuff and Escape sequences were better known when the book was written or do the authors assume too much with their strong UNIX background?