How to prevent a letter insert in a int var ?

[YUS]

Hi,
I've got a problem.

I have a program that ask for a number to the user.
If the user put a letter instead of a number the program crashes (loop).

How can I prevent this ?
I've tried with isdigit but with no results.

int choise;

cout << "\nChoose one: ";
cin >> setw(sizeof(choice)) >> choise;
if(isdigit(choice)) cout <<"all ok";
if(isalpha(choice)) cout<<"error - number needed";

but the code doesn't work.
=(

Thanks to all.

--
oooO Oooo
( ) YUS ( )
\ ( Para todos, todo, ) /
\_ ) nada para nosotros. ( _/

[Alf P. Steinbach]

* YUS:

I've got a problem.

I have a program that ask for a number to the user.
If the user put a letter instead of a number the program crashes (loop).

How can I prevent this ?
I've tried with isdigit but with no results.

int choise;

cout << "\nChoose one: ";
cin >> setw(sizeof(choice)) >> choise;
if(isdigit(choice)) cout <<"all ok";
if(isalpha(choice)) cout<<"error - number needed";

but the code doesn't work.

Consider that attempted conversion to 'int' has already happened by the
time you call 'isdigit' and 'isalpha'.

Instead check the error state of the stream.

--
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?

[YUS]

Alf P. Steinbach wrote:

Consider that attempted conversion to 'int' has already happened by
the time you call 'isdigit' and 'isalpha'.

Instead check the error state of the stream.

Sorry but.. how ???
:p
I really got no idea!

--
oooO Oooo
( ) YUS ( )
\ ( Para todos, todo, ) /
\_ ) nada para nosotros. ( _/

[Gavin Deane]

YUS wrote:

Alf P. Steinbach wrote:

Consider that attempted conversion to 'int' has already happened by
the time you call 'isdigit' and 'isalpha'.

Instead check the error state of the stream.

Sorry but.. how ???
:p
I really got no idea!

http://www.parashift.com/c++-faq-lit....html#faq-15.2

Gavin Deane

[Howard]

"YUS" <mo******@NOSPAMtin.it> wrote in message
news:43***********************@reader1.news.tin.it ...

Hi,
I've got a problem.

I have a program that ask for a number to the user.
If the user put a letter instead of a number the program crashes (loop).

How can I prevent this ?
I've tried with isdigit but with no results.

int choise;

cout << "\nChoose one: ";
cin >> setw(sizeof(choice)) >> choise;
if(isdigit(choice)) cout <<"all ok";
if(isalpha(choice)) cout<<"error - number needed";

but the code doesn't work.
=(

A common solution is to always enter data into a std::string, and then see
if the string can be converted into an integer (or double or whatever). If
it cannot be converted, then tell the user there's an error and loop back to
allow them to re-enter the data.

-Howard

[Mike Wahler]

"YUS" <mo******@NOSPAMtin.it> wrote in message
news:43***********************@reader1.news.tin.it ...

Hi,
I've got a problem.

I have a program that ask for a number to the user.
If the user put a letter instead of a number the program crashes (loop).

How can I prevent this ?
I've tried with isdigit but with no results.

int choise;

cout << "\nChoose one: ";
cin >> setw(sizeof(choice)) >> choise;
if(isdigit(choice)) cout <<"all ok";
if(isalpha(choice)) cout<<"error - number needed";

but the code doesn't work.
Look again at the documentation for 'isdigit()'.
It doesn't do what you apparently believe.
=(

#include <istream>
#include <iostream>
#include <sstream>
#include <string>

int get_int()
{
int result(0);
std::string text;
std::istringstream iss;;

do
{
std::cout << "Enter an integer value: ";
std::cin >> text;
iss.clear();
iss.str(text);

if(!(iss >> result))
std::cerr << " * Not a valid integer value\n";

} while(!iss);

return result;
}

int main()
{
int i(0);

i = get_int();
std::cout << "You entered: " << i << '\n';
return 0;
}

-Mike

[YUS]

YUS wrote:

Thanks to all.

I repeat, thanks to all guys =)
Very useful.

--
oooO Oooo
( ) YUS ( )
\ ( Para todos, todo, ) /
\_ ) nada para nosotros. ( _/