is this simple program correct? K&R 1-12

This is a discussion on is this simple program correct? K&R 1-12 within the C Programming forums, part of the General Programming Boards category; This is how I solved the exercise 1-12 from K&R. I have found another solution online, but mine seems a ...

  1. #1
    fsx
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    is this simple program correct? K&R 1-12

    This is how I solved the exercise 1-12 from K&R. I have found another solution online, but mine seems a lot easier than the other, even if sometimes it prints too many newlines.
    Is this solution acceptable? If not, why? Thank you in advance.

    FSX

    Code:
    #include <stdio.h>
    
    int main(void)
    {
    	int c;
    
    	while((c = getchar()) != EOF)
    	{
    		if((c == ' ') || (c == '\t'))
    			putchar('\n');
    		else
    			putchar(c);
    	}
    	return 0;
    }

  2. #2
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    Quote Originally Posted by fsx View Post
    Is this solution acceptable? If not, why?
    Since your program is not a correct solution, it is especially not acceptable. Re-read the exercise: "Write a program that prints its input one word per line." Your program occasionally prints empty lines, i.e. lines that don't contain a word (and certainly K&R weren't thinking about the empty word here).

    Try to get rid of these empty lines, e.g. by introducing two states "last character was a whitespace" and "last character wasn't". Also have a look at the isspace() function/macro.

    mine seems a lot easier than the other, even if sometimes it prints too many newlines.
    If you allow your program to occasionally produce incorrect results, here's an even simpler version:

    Code:
    int main() {}
    ;-),
    Philip
    All things begin as source code.
    Source code begins with an empty file.
    -- Tao Te Chip

  3. #3
    DESTINY BEN10's Avatar
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    Quote Originally Posted by fsx View Post
    This is how I solved the exercise 1-12 from K&R. I have found another solution online, but mine seems a lot easier than the other, even if sometimes it prints too many newlines.
    Is this solution acceptable? If not, why? Thank you in advance.

    FSX

    Code:
    #include <stdio.h>
    
    int main(void)
    {
    	int c;
    
    	while((c = getchar()) != EOF)
    	{
    		if((c == ' ') || (c == '\t'))
    			putchar('\n');
    		else
    			putchar(c);
    	}
    	return 0;
    }
    i executed ur code and it seems to me its working properly.i simply inputted a line and it gave me each word of the line in a new line.

  4. #4
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    Try inputting two or more lines, Ben. You'll see the code prints additional blank lines.

    In any event, fsx, Snafuist is right - printing additional unwanted output hardly qualifies as a correct solution. The objective of writing code is to deliver the required functionality: no more, no less. Having code that is "easier" is not an excuse for delivering slightly different functionality. The programmer is expected to meet requirements, not force the user to accept compromised requirements.

  5. #5
    spurious conceit MK27's Avatar
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    Quote Originally Posted by fsx View Post
    Code:
    	while((c = getchar()) != EOF)
    	{
    		if((c == ' ') || (c == '\t'))
    			putchar('\n');
    What you really want is a "nop" (no-op, no operation) and to continue --
    Code:
    		if((c == ' ') || (c == '\t'))
    			continue;
    Except you still need a line break! So maybe
    Code:
    #include <stdio.h>
    
    int main(void)
    {
    	int c;
    	char flag=0;
    
    	while((c = getchar()) != EOF)
    	{
    		if((c == ' ') || (c == '\t'))
    			if (flag) continue;
    			else { putchar('\n');
    				flag=1; }
    		else {	putchar(c);
    			flag=0; }
    	}
    	return 0;
    }
    If you are just on chapter 1 you may not know about "continue" (it just starts the loop again without doing anything else).

    The use of a flag is a very handy, basic, chapter 1 kind of thing, so if you don't understand what that's about, try to, or ask and I'll explain.

    Basically now you could type:
    Code:
    this       is     a   sentance   with  extra      spaces
    Output:
    this
    is
    a
    sentence
    with
    extra
    spaces
    
    C programming resources:
    GNU C Function and Macro Index -- glibc reference manual
    The C Book -- nice online learner guide
    Current ISO draft standard
    CCAN -- new CPAN like open source library repository
    3 (different) GNU debugger tutorials: #1 -- #2 -- #3
    cpwiki -- our wiki on sourceforge

  6. #6
    Frequently Quite Prolix dwks's Avatar
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    That was the idea that Snafuist introduced at the beginning. I think you could come up with a better name than "flag" for that variable, though. Maybe something like "saw_whitespace". There's also a logical bug in the program (which was present in my first version too): since the flag is initially zero, there will be a blank line at the beginning of the output if the first character is whitespace. Also, continue isn't really necessary.

    Anyway, here's my shot at it.
    Code:
    #include <stdio.h>
    #include <ctype.h>
    
    int main() {
        int c, between_words = 1;
    
        while((c = getchar()) != EOF) {
            if(isspace(c)) {
                if(!between_words) {
                    putchar('\n');
                    between_words = 1;
                }
            }
            else {
                putchar(c);
                between_words = 0;
            }
        }
    
        return 0;
    }
    Note the use of isspace() from ctype.h. isspace [C++ Reference]
    dwk

    Seek and ye shall find. quaere et invenies.

    "Simplicity does not precede complexity, but follows it." -- Alan Perlis
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  7. #7
    fsx
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    I am still stumbling...


    Code:
    #include <stdio.h>
    
    int main(void)
    {
    	int c, pc;
    
    	while((c = getchar()) != EOF)
    	{
    		if((c == ' ') || (c == '\t') && (pc != c))
    			putchar('\n');
    		else if((c != ' ') && (c != '\t'))
    			putchar(c);
    		else
    			putchar(c);
    		pc = c;
    	}
    	return 0;
    }

  8. #8
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    What is not working?

    I would expect that you will need a nested if-statement:
    Code:
       if (c == ' ' || c == '\t')
       {
         if (pc != c)
           putchar('\n');
       }
       else 
           putchar(c);
    This will prevent multiple spaces from giving multiple newlines.

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

  9. #9
    fsx
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    Thanks a lot! What I would like to understand is why if I use the && it doesn't works... shouldn't it be similar to another IF statement?

    Quote Originally Posted by matsp View Post
    What is not working?

    I would expect that you will need a nested if-statement:
    Code:
       if (c == ' ' || c == '\t')
       {
         if (pc != c)
           putchar('\n');
       }
       else 
           putchar(c);
    This will prevent multiple spaces from giving multiple newlines.

    --
    Mats

  10. #10
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    Because you do not want the ELSE part to be executed if the second if is false - only if the first if is false.

    You could of course add a "if (pc != c)" inside the else-branch instead, but that's less logical.

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

  11. #11
    spurious conceit MK27's Avatar
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    Quote Originally Posted by dwks View Post
    That was the idea that Snafuist introduced at the beginning. I think you could come up with a better name than "flag" for that variable, though.
    I called it "flag" because it is a (boolean) flag and I wanted the OP (fsx) to pick up on that (Snafuist refers to this as "two states", which is not quite as specific -- I guess you could see a boolean flag as an implementation of a two-state concept).

    You're right about the continue being unnecessary and the initial whitespace issue.

    Here's a related question: I usually use a char for boolean values cause it's smaller, but would it be true that an int is actually faster for the processor because it has a four byte boundary? Sort of nit-picking, but this could have a lot of significance in the right place...
    C programming resources:
    GNU C Function and Macro Index -- glibc reference manual
    The C Book -- nice online learner guide
    Current ISO draft standard
    CCAN -- new CPAN like open source library repository
    3 (different) GNU debugger tutorials: #1 -- #2 -- #3
    cpwiki -- our wiki on sourceforge

  12. #12
    CSharpener vart's Avatar
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    Quote Originally Posted by MK27 View Post
    Here's a related question: I usually use a char for boolean values cause it's smaller, but would it be true that an int is actually faster for the processor because it has a four byte boundary? Sort of nit-picking, but this could have a lot of significance in the right place...
    yes it could. you need profiling to prove it or opposite (when the cache size is critical issue)
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

  13. #13
    fsx
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    Quote Originally Posted by matsp View Post
    Because you do not want the ELSE part to be executed if the second if is false - only if the first if is false.

    You could of course add a "if (pc != c)" inside the else-branch instead, but that's less logical.

    --
    Mats
    Mats got exactly what I was looking for, a simple explanation. I'm new to C and all those pointers, includes and so on are totally alien to my current knowledge. But thanks also for the other answerers.

  14. #14
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    Quote Originally Posted by MK27 View Post
    Here's a related question: I usually use a char for boolean values cause it's smaller, but would it be true that an int is actually faster for the processor because it has a four byte boundary? Sort of nit-picking, but this could have a lot of significance in the right place...
    Can't bit fields be used for this (making the int size smaller) ? Or is the struct making it larger again?

    Code:
    #include<stdio.h>
    
    struct foo
    {
    	int flag:2;
    } bar;
    
    int main(void)
    {
    	bar.flag = 1;
    	printf("%d", bar.flag);
    	
    	return 0;
    }
    Operating Systems:
    - Ubuntu 9.04
    - XP

    Compiler: gcc

  15. #15
    ATH0 quzah's Avatar
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    Bitfields won't actually shrink the structure smaller than the actual type. That is to say, even if you set up a bit field of :2, it's still going to be at least an int in size.

    Quzah.
    Hope is the first step on the road to disappointment.

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