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exercise 1-20 K&R

 
 
Aenima1891
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Posts: n/a
 
      06-10-2006
write a program that replaces strings of blanks by the minimum number
of blanks to space to the next tab stop.

#include <stdio.h>
#define TABSIZE 8


int main()
{
int counter, c;

while ((c = getchar()) != EOF) {
if (c == '\t') {
for (counter = 1; counter <= TABSIZE; ++counter)
putchar(' ');
}
else
putchar(c);
}
return 0;
}

what do you think about this??

 
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Robert Gamble
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      06-10-2006
Aenima1891 wrote:
> write a program that replaces strings of blanks by the minimum number
> of blanks to space to the next tab stop.
>
> #include <stdio.h>
> #define TABSIZE 8
>
>
> int main()


int main (void) is preferred.

> {
> int counter, c;
>
> while ((c = getchar()) != EOF) {
> if (c == '\t') {
> for (counter = 1; counter <= TABSIZE; ++counter)
> putchar(' ');


This doesn't accomplish the goal of the exercise which is to replace
the tab with the number of spaces needed for the *next* tab stop, that
is, the next multiple of TABSIZE characters. Your version always
prints TABSIZE spaces which will only be the right thing to do when the
tab character is encountered immemdiately after a tab stop.

> }
> else
> putchar(c);
> }
> return 0;
> }
>
> what do you think about this??


Robert Gamble

 
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Michael Mair
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Posts: n/a
 
      06-10-2006
Aenima1891 schrieb:
> write a program that replaces strings of blanks by the minimum number
> of blanks to space to the next tab stop.
>
> #include <stdio.h>
> #define TABSIZE 8
>
>
> int main()


int main (void)

> {
> int counter, c;


Note: It often helps understanding to separate variable declarations
by "purpose" and not only by type. counter is used just as that,
whereas c is intended to hold a character[*].
This also makes for easier maintenance if you find out that the
_guaranteed_ range of int is not sufficient for your purposes and
you have to switch to long, unsigned long or size_t as counter type.
int counter, anotherCounter;
int c, anotherTempForCharacters;
int resultOfSomeNoncounterCalculation;

Some company coding standards even forbid declaring more than one
variable per line if the declared variables are not loop variables.


> while ((c = getchar()) != EOF) {
> if (c == '\t') {
> for (counter = 1; counter <= TABSIZE; ++counter)
> putchar(' ');


You misunderstood the purpose of the task.
Every _line_ is to be formatted independently of the other. For every
line, you start anew with tab stops. This means that you need a
character count for the current line, not an overall character count.

Tab stops are at the same character number (modulo TABSIZE) throughout
the line, i.e. you insert space characters until your counter modulo
TABSIZE equals that number.

Example: For "#define TABSIZE 4",
"\ta\tab\tabc\tabcd\tabcde\t\n" has to become either
" a ab abc abcd abcde \n"
^ ^ ^ ^ ^ ^ ^ ^ ^
where the second line indicates the tab stop positions for clarity.

Or, if you admit the possibility of inserting 0 spaces to fit the
description, your result would be
"a ab abc abcdabcde \n"
^ ^ ^ ^ ^ ^ ^
This is merely the difference between a while() and a do--while()
loop (figure out which one for which case yourself) for you.

> }
> else
> putchar(c);
> }
> return 0;
> }
>
> what do you think about this??

[*] To be more precise: A character cast to unsigned char or EOF.
This is what you typically pass to putchar(), [f]putc() and the
is....() functions and get from getchar(), etc.


Cheers
Michael
--
E-Mail: Mine is an /at/ gmx /dot/ de address.
 
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