converting a character in a string to an integer

[ross.oneill]

Hi,

I have a string
strcpy(str, "2A");

and I want to grab the char 2 and convert it to an integer.

I tried doing this

int num = atoi(str[0]);

and it will not compile.

Any suggestions

Thanks
-R

 

[Walter Roberson]

I have a string
strcpy(str, "2A");

and I want to grab the char 2 and convert it to an integer.

I tried doing this

int num = atoi(str[0]);

and it will not compile.

atoi() must be passed a const char *str, but str[0] is just a plain char.
Even with automatic promotion into a const char, that's still a difference
of char vs pointer-to-char .

What is your general rule for such inputs? That there is -exactly-
one digit, which will be followed by something that is not a digit?
That you only want to convert one digit no matter what follows
(including possibly another digit)? That there might be several
digits, followed by something that is not a digit?

atoi() stops parsing when it finds something that isn't a valid
digit... but watch out for the boundary case where the input
does not start start with a digit. See also strtoul() and kin,
which have much better error reporting.

If you have exactly one digit, you could just use
int num = str[0]-'0';

 

[pete]

I have a string
strcpy(str, "2A");

and I want to grab the char 2 and convert it to an integer.

I tried doing this

int num = atoi(str[0]);

and it will not compile.

What is your general rule for such inputs? That there is -exactly-
one digit, which will be followed by something that is not a digit?
That you only want to convert one digit no matter what follows
(including possibly another digit)?

If that's the rule, then it's simple.

int num = "2A"[0] - '0';

 

[Barry Schwarz]

Hi,

I have a string
strcpy(str, "2A");

and I want to grab the char 2 and convert it to an integer.

I tried doing this

int num = atoi(str[0]);

What type of argument does atoi take? What is the type of str[0]? If
the value in str had been "29", would you still want only the 2?

and it will not compile.

<<Remove the del for email>>

 

[pemo]

I have a string
strcpy(str, "2A");

and I want to grab the char 2 and convert it to an integer.

I tried doing this

int num = atoi(str[0]);

and it will not compile.

What is your general rule for such inputs? That there is -exactly-
one digit, which will be followed by something that is not a digit?
That you only want to convert one digit no matter what follows
(including possibly another digit)?

If that's the rule, then it's simple.

int num = "2A"[0] - '0';

Nice.