strcmp() And if

[Eirik]

Shouldn't this code work? If not, why shouldn't it?

#include <stdio.h>

int main(void)

{

char yesno[10];
char *yes = "yes";
char *no = "no";

printf("Select: yes or no\n");
fgets(yesno, sizeof(yesno), stdin);

if(strcmp(yes, yesno) == 0)
{
printf("yes\n") ;
}
if(strcmp(no, yesno) == 0)
{
printf("no\n");
}

return 0;

}

[Anupam]

Lew Pitcher <lp******@sympa tico.ca> wrote in message news:<53******* ****@merlin.l6s 4x6-4.ca>...

Eirik wrote:

Shouldn't this code work? If not, why shouldn't it?

#include <stdio.h>

int main(void)

{

char yesno[10];
char *yes = "yes";
Here, your yes variable is a pointer to a four character array, such that

Nitpick :: The yes variable is a pointer to a character .. specifically to
the first character in the string "yes". No type information is stored in
it. The declaration for a pointer to a four character array would be :
char (* p4array)[4];
*(yes+0) == 'y'
*(yes+1) == 'e'
*(yes+2) == 's' and
*(yes+3) == '\0'

char *no = "no";
Similarly, your no variable is a pointer to a three character array, such that

Likewise.
*(no+0) == 'n'
*(no+1) == 'o' and
*(no+2) == '\0'

printf("Select: yes or no\n");
fgets(yesno, sizeof(yesno), stdin);

fgets() stops reading after an EOF or a newline. If a newline is read, it is
stored in the buffer. A \0 is stored after the last character in the buffer.

If your hosted environment is consistant with most environments, fgets() will
have captured a buffer that
a) has a newline character following the input data, and
b) has a \0 after the newline character.

Assuming the user entered "no", then yesno will be string of four characters
yesno[0] will be 'n'
yesno[1] will be 'o'
yesno[2] will be '\n' and
yesno[3] will be '\0'

if(strcmp(yes, yesno) == 0)

strcmp() performs a character by character comparison. Even if the user entered
"yes", if the entry was terminated by a newline, then yesno will carry "yes\n",
but yes will point to a string "yes". These are not equal (yesno carries a '\n'
where yes carries a '\0'), and the test fails.

{
printf("yes\n") ;
}
if(strcmp(no, yesno) == 0)

Similarly, if the user entered "no", and the entry was terminated by a newline,
then yesno will carry "no\n", but no will point to the string "no". Again, the
comparison fails because '\n' is not equal to '\0'.

{
printf("no\n");
}

return 0;

}

One way to fix this would be to change

> char *yes = "yes";
> char *no = "no";

to

char *yes = "yes\n";
char *no = "no\n";

[Lew Pitcher]

Anupam wrote:

Lew Pitcher <lp******@sympa tico.ca> wrote in message news:<53******* ****@merlin.l6s 4x6-4.ca>...

Eirik wrote:

Shouldn't this code work? If not, why shouldn't it?

#include <stdio.h>

int main(void)

{

char yesno[10];
char *yes = "yes";

Here, your yes variable is a pointer to a four character array, such that

Nitpick :: The yes variable is a pointer to a character .. specifically to
the first character in the string "yes". No type information is stored in
it. The declaration for a pointer to a four character array would be :
char (* p4array)[4];

Yes, of course. :-)
My only excuse is that I tried to simplify the explanation somewhat.
[snip]

--
Lew Pitcher

Master Codewright and JOAT-in-training
Registered Linux User #112576 (http://counter.li.org/)
Slackware - Because I know what I'm doing.