atoi question

[Rick]

Hi,

Another newbie question. I'm trying to convert a char to an integer. My
input is a string which holds a number on place 4. However, if I try
int number = atoi( input[3] );
I'll get an error because of the type conversion I guess. Atoi wants a
string while I put a single char into it. So I tried it another way:
char s[2];
int number;
s[0] = input[3];
s[1] = 0;
number = atoi( s );

That worked but aren't their better ways?

Greetings,
Rick

[Christopher Benson-Manica]

Rick <as******@hotma il.com> spoke thus:

Another newbie question. I'm trying to convert a char to an integer. My
input is a string which holds a number on place 4. However, if I try
int number = atoi( input[3] );

int number=atoi( input+3 );

--
Christopher Benson-Manica | I *should* know what I'm talking about - if I
ataru(at)cybers pace.org | don't, I need to know. Flames welcome.

[Rick]

Yes, that's what I call a better way! Thanks!

Rick

[Karl Heinz Buchegger]

Rick wrote:

Hi,

Another newbie question. I'm trying to convert a char to an integer. My
input is a string which holds a number on place 4. However, if I try
int number = atoi( input[3] );
I'll get an error because of the type conversion I guess. Atoi wants a
string while I put a single char into it. So I tried it another way:
char s[2];
int number;
s[0] = input[3];
s[1] = 0;
number = atoi( s );

That worked but aren't their better ways?

int number = input[3] - '0';
--
Karl Heinz Buchegger
kb******@gascad .at

[Dan Pop]

In <3f************ ***********@new s.xs4all.nl> "Rick" <as******@hotma il.com> writes:

Another newbie question. I'm trying to convert a char to an integer. My
input is a string which holds a number on place 4. However, if I try
int number = atoi( input[3] );
I'll get an error because of the type conversion I guess. Atoi wants a
string while I put a single char into it. So I tried it another way:
char s[2];
int number;
s[0] = input[3];
s[1] = 0;
number = atoi( s );

That worked but aren't their better ways?

For single digit conversions, subtracting '0' (quotes included) from the
char value is guaranteed to provide the correct result, as long as the
char value really corresponds to a digit. In other words, C guarantees
that the value of each digit is one greater than the value of the previous
regardless of the character set used by the implementation.

Note that the usage of atoi is usually restricted to newbies or to those
cases where the string is known to contain a valid number: its behaviour
on erroneous input is suboptimal.

Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Da*****@ifh.de

[Mark Gordon]

On Mon, 27 Oct 2003 13:54:06 +0100
"Rick" <as******@hotma il.com> wrote:

Another newbie question. I'm trying to convert a char to an integer.
My input is a string which holds a number on place 4. However, if I
try
int number = atoi( input[3] );
I'll get an error because of the type conversion I guess. Atoi wants a
string while I put a single char into it. So I tried it another way:
char s[2];
int number;
s[0] = input[3];
s[1] = 0;
number = atoi( s );

That worked but aren't their better ways?

That depends on what you mean by "convert a char to an integer". If you
want to convert a single character in the range '0' to '9' then
int val='5'-'0'; /* val is guaranteed to be 5 */
So for your example
/* do some data validation */
number = input[3] - '0';

NOTE: The whilst the ordering of characters '0' to '9' is guaranteed by
the standard the rest of the character set has no such guarantee so, for
example, reporting which letter of the alphabet 'c' is requires
something a bit more than 1 + 'c' - 'a'
--
Mark Gordon
Paid to be a Geek & a Senior Software Developer
Although my email address says spamtrap, it is real and I read it.

[Rick]

Everyone thanks again!

Rick

[Isaac Mushinsky]

Christopher Benson-Manica wrote:

Rick <as******@hotma il.com> spoke thus:

Another newbie question. I'm trying to convert a char to an integer. My
input is a string which holds a number on place 4. However, if I try
int number = atoi( input[3] );

int number=atoi( input+3 );

Sis you mean a digit at postion 3? Or a null-termnated number starting at
intput+3? This will fail in the case of a single digit unless input[4] is
null.