Stroustrup 5.9, exercise 10 (using a function)

[arnuld]

this does not work, i know there is some problem in the "for loop" of
"print_arr" function. i am not able to correct the weired results i am
getting. i have no compile time error, it is only semantic-bug that is
causing the trouble:

EXPECTED: january, february, march....decemb er
GOT: january, january, january........ .january

------------- PROGRAMME --------------
/* Stroustrup, 5.9, exercise 10

STATEMENT:
define an array of strings,where strings contains the names months .
Print those strings. Pass the array to a function that prints those
strings.

SOLUTION:

1.) 1st, i will print array int he "main" using "for" loop and array
indexing.

2.) then i wil print he array using a function and passing the array
to the function as argument(pass by reference).

NOTICE: posted code is implementation of (2)
*/

#include<iostre am>

void print_arr(const char**, size_t);

int main()
{
const char* arr[] = {"january", "february", "march", "april", "may",
"june",
"july", "august", "september" , "october",
"november",
"december"} ;

const size_t arr_size = sizeof(arr) / sizeof(*arr);

print_arr(arr, arr_size);

return 0;

}

void print_arr(const char** arr, size_t arr_size)
{
const char** p = arr;

std::cout << "\n\tUSING FUNCTION\n";
for(unsigned int i=0; i < arr_size; ++i)
std::cout << *p << std::endl;

}

-------------- OUTPUT ----------------------
[arch@voodo tc++pl]$ g++ -ansi -pedantic -Wall -Wextra 5.9_ex-10-
function.cpp
[arch@voodo tc++pl]$ ./a.out

USING FUNCTION
january
january
january
january
january
january
january
january
january
january
january
january
[arch@voodo tc++pl]$

[arnuld]

On Apr 2, 12:39 pm, Michael DOUBEZ <michael.dou... @free.frwrote:

Using pointer arithmetic, you forgot to increment p; use:
for(unsigned int i=0; i < arr_size; ++i,++p)

You can also use arr instead or just deference it:
for(unsigned int i=0; i < arr_size; ++i)
std::cout << arr[i] << std::endl;

Michael

OOPS!, sorry

[arnuld]

OK, i have a little of improvement. what do you say?

--------- PROGRAMME ------------
/* Stroustrup, 5.9, exercise 10

STSTAMENT:
define an array of strings,where strings contains the names months
.. Print those strings. Pass the array to a function that prints those
strings.
SOLUTION:

1.) 1st, i will print array int he "main" using "for" loop
and array indexing.

2.) then i wil print he array using a function and passing the array
to the function as argument(pass by reference).
NOTICE: posted code is implementation of (2)
*/

#include<iostre am>

void print_arr(const char**);

int main()
{
const size_t MonthsInYear = 12;

const char* arr[MonthsInYear + 1] =
{"january", "february", "march", "april", "may", "june",
"july", "august", "september" , "october", "november",
"december", '\0'};
print_arr(arr);

return 0;
}
void print_arr(const char** arr)
{
std::cout << "\n\tUSING FUNCTION\n";
for(const char** p = arr; *p != '\0' ; ++p)
std::cout << *p << std::endl;
}

--------- OUTPUT -------------
[arch@voodo tc++pl]$ g++ -ansi -pedantic -Wall -Wextra -O 5.9_ex-10-
function.cpp
[arch@voodo tc++pl]$ ./a.out

USING FUNCTION
january
february
march
april
may
june
july
august
september
october
november
december
[arch@voodo tc++pl]$

[=?iso-8859-1?q?Erik_Wikstr=F6m?=]

On 2 Apr, 10:07, "arnuld" <geek.arn...@gm ail.comwrote:

OK, i have a little of improvement. what do you say?

--------- PROGRAMME ------------
/* Stroustrup, 5.9, exercise 10

STSTAMENT:
define an array of strings,where strings contains the names months
. Print those strings. Pass the array to a function that prints those
strings.

SOLUTION:

1.) 1st, i will print array int he "main" using "for" loop
and array indexing.

2.) then i wil print he array using a function and passing the array
to the function as argument(pass by reference).

NOTICE: posted code is implementation of (2)
*/

#include<iostre am>

void print_arr(const char**);

int main()
{
const size_t MonthsInYear = 12;

const char* arr[MonthsInYear + 1] =
{"january", "february", "march", "april", "may", "june",
"july", "august", "september" , "october", "november",
"december", '\0'};

print_arr(arr);

return 0;

}

void print_arr(const char** arr)
{
std::cout << "\n\tUSING FUNCTION\n";
for(const char** p = arr; *p != '\0' ; ++p)
std::cout << *p << std::endl;

}

Personally I'd prefer a version where the size is passed as an
argument just to be safe, something like your first try, but also
incrementing arr:

void print_arr(const char** arr, size_t arr_size)
{
std::cout << "\n\tUSING FUNCTION\n";
for(unsigned int i=0; i < arr_size; ++i, arr++)
std::cout << *arr << std::endl;

}

--
Erik Wikström

[arnuld]

On Apr 2, 1:47 pm, "Erik Wikström" <eri...@student .chalmers.sewro te:

Personally I'd prefer a version where the size is passed as an
argument just to be safe, something like your first try, but also
incrementing arr:

void print_arr(const char** arr, size_t arr_size)
{
std::cout << "\n\tUSING FUNCTION\n";
for(unsigned int i=0; i < arr_size; ++i, arr++)
std::cout << *arr << std::endl;

}

this is the 1st time i have seen someone incrementing an "array",
never saw so even in any book. does it work like this:

*arr == &arr[0]
++arr == &arr[0 + 1]

?

IOW, like a pointer

[=?iso-8859-1?q?Erik_Wikstr=F6m?=]

On 2 Apr, 11:00, "arnuld" <geek.arn...@gm ail.comwrote:

On Apr 2, 1:47 pm, "Erik Wikström" <eri...@student .chalmers.sewro te:
Personally I'd prefer a version where the size is passed as an
argument just to be safe, something like your first try, but also
incrementing arr:

void print_arr(const char** arr, size_t arr_size)
{
std::cout << "\n\tUSING FUNCTION\n";
for(unsigned int i=0; i < arr_size; ++i, arr++)
std::cout << *arr << std::endl;

}

this is the 1st time i have seen someone incrementing an "array",
never saw so even in any book. does it work like this:

*arr == &arr[0]
++arr == &arr[0 + 1]

?

IOW, like a pointer

Yes, arr[N] is the same as *(arr[0] + N) == *(arr + N).

The following might help you understand but should *never* be used in
real life, read the rest at your own risk:
Using the transitivity of addition (meaning that A+B == B+A) we can
get some pretty ugly, but valid, syntax when indexing into arrays:

So arr[N] == *(arr + N) then we apply the transitivity rule on the
left hand giving *(N + arr) and then go back to the array-form gives
N[arr].

So given array arr then 2[arr] will give the third element in arr. And
then we replace the N with a variable and we get something like this:

int main()
{
int arr[3] = {1, 2, 3};
for (int i = 0; i < 3; ++i)
std::cout << i[arr];
return 0;
}

--
Erik Wikström

[Alf P. Steinbach]

* Erik Wikström:

>
Using the transitivity of addition (meaning that A+B == B+A)

ITYM commutativity.

--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?

[=?iso-8859-1?q?Erik_Wikstr=F6m?=]

On 2 Apr, 11:40, "Alf P. Steinbach" <[e-mail] rote:

* Erik Wikström:

Using the transitivity of addition (meaning that A+B == B+A)

ITYM commutativity.

Ah, yes.

--
Erik Wikström

[Default User]

arnuld wrote:

OK, i have a little of improvement. what do you say?

const char* arr[MonthsInYear + 1] =
{"january", "february", "march", "april", "may", "june",
"july", "august", "september" , "october", "november",
"december", '\0'};

void print_arr(const char** arr)
{
std::cout << "\n\tUSING FUNCTION\n";
for(const char** p = arr; *p != '\0' ; ++p)
std::cout << *p << std::endl;
}

I don't like the use of '\0' there. While it's technically not wrong,
as that's a legitimate null pointer constant, I think it betrays a lack
of understanding on your part.

That last element of the array is NOT a character, particularly it is
not a character like the null terminator in a character array (C-style
string).

What you want in this case for an array terminator is a null pointer.
I'd prefer the use of a plain 0, or even NULL (although many in the C++
community don't care for that macro).


Brian

[arnuld]

On Apr 2, 9:55 pm, "Default User" <defaultuse...@ yahoo.comwrote:

I don't like the use of '\0' there. While it's technically not wrong,
as that's a legitimate null pointer constant, I think it betrays a lack
of understanding on your part.

:-(

That last element of the array is NOT a character, particularly it is
not a character like the null terminator in a character array (C-style
string).

well, its a new thing you told :-)

What you want in this case for an array terminator is a null pointer.
I'd prefer the use of a plain 0, or even NULL (although many in the C++
community don't care for that macro).

OK, 0 (zero) then

Brian