Character handling help

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11-21-2003
vandalay

Character handling help

I've been workin on the following program and could use a little help. The program should input a character from the keyboard and using isdigit, return wheter the character is a digit or not. The program compiles fine, but will not function. I get a program error and the window is closed. I also tried to input the character into the isdigit function as a pointer to character and that also would not work.

Code:

#include <stdio.h> #include <ctype.h> int main() { int character; /* Initializes character */ printf( "Enter a character: "); /* Asks for character and inputs it */ scanf( "%d", character ); /* This should determine if the character is a digit or not */ printf( "%d%s", isdigit( character ) ? "The character is a " : "The character is not a ", "digit." ); return 0; }

Thanks!
11-21-2003
XSquared

You're missing the number. According to the first argument you're passing to printf, it expects a number and a string. You're just passing a string.
11-22-2003
Shiro

Code:

printf( "%d%s", isdigit( character ) ? "The character is a " : "The character is not a ", "digit." );

Here printf() expects an integer and a string. You are passing two strings. If character is a digit, then the first string is "The character is a", else the first string is "The character is not a". the second string is "digit.".

Also you expect a character, so variable character could be of type char and you should read a character.

Code:

char character; scanf( "%c", &character);
11-22-2003
vandalay

Thanks for the help.
11-23-2003
vandalay

Any ideas on how I can get the program to take whitespace characters and test them as well? I'm able to enter and check single characters, but it needs to check short strings also.
11-23-2003
Salem

Generally speaking, you should always use fgets() to read the input into a buffer.

Then you have all the freedom to use as many buffer oriented functions (including sscanf()) to extract information from that buffer.
11-23-2003
vandalay

Quote:

Originally posted by Salem
Generally speaking, you should always use fgets() to read the input into a buffer.

Then you have all the freedom to use as many buffer oriented functions (including sscanf()) to extract information from that buffer.

I havent quite worked my way up to that yet. Any suggestions using arrays or pointers?
11-23-2003
WaltP

Quote:

Originally posted by vandalay
I havent quite worked my way up to that yet. Any suggestions using arrays or pointers?

scanf() is so full of problems when dealing with mixed input (numbers, strings, whitespace) that you will spend a LOT of time trying to figure it out, then when you learn how to use fgets() you will see a much better way to handle input. YOU have the control instead of cobbling together unreadable format specifiers. If you must, learn scanf() fully. But I'd recommend either waiting for fgets() and learn how to parse a string then, or look into fgets() now... Beat the rush.
11-23-2003
kermit

Quote:

Originally posted by vandalay
Any ideas on how I can get the program to take whitespace characters and test them as well? I'm able to enter and check single characters, but it needs to check short strings also.

I am assuming that because you know of isdigit() you also are aware of isspace()?

~/
11-23-2003
vandalay

Quote:

Originally posted by kermit
I am assuming that because you know of isdigit() you also are aware of isspace()?

~/

Thats the part of the program I'm having trouble with. I'm unable to enter a string such as \n or \t to test to see if its a whitespace character. I'm only able to enter a single character. When \n is entered, only \ is tested.
11-23-2003
kermit

Is there a reason why you could not use the getchar() function? It works nicely for such things.

Code:

#include <stdio.h> #include <ctype.h> int main( void ) { int *character; /* Initializes character */ printf( "Enter a character: "); /* Asks for character and inputs it */ *character = getchar(); /* This should determine if the character is a digit or not */ printf( "\n%s%s", isdigit( *character ) ? "The character is a " : "The character is not a ", "digit.\n\n" ); return 0; }

[edit]
Sorry, I should have paid better attention - the digit thing was solved, you need to know about spaces now. You can do that with getchar too, but using fgets() might be your bets bet, as was previously mentioned, as the stuff is already nicely in a buffer for you, and you can do any test on the contents of the buffer you desire.
~/
11-23-2003
vandalay

Quote:

Originally posted by kermit
Is there a reason why you could not use the getchar() function? It works nicely for such things.

Code:

#include <stdio.h> #include <ctype.h> int main( void ) { int *character; /* Initializes character */ printf( "Enter a character: "); /* Asks for character and inputs it */ *character = getchar(); /* This should determine if the character is a digit or not */ printf( "\n%s%s", isdigit( *character ) ? "The character is a " : "The character is not a ", "digit.\n\n" ); return 0; }

[edit]
Sorry, I should have paid better attention - the digit thing was solved, you need to know about spaces now. You can do that with getchar too, but using fgets() might be your bets bet, as was previously mentioned, as the stuff is already nicely in a buffer for you, and you can do any test on the contents of the buffer you desire.
~/

Thanks Kermit. I tried your suggestion and still only get the \ of \n or \t to test against isspace. Any other recommendations?
11-23-2003
kermit

Could you possibly give a little context as to what you want to do with this input, and why you are testing for a space? It might be helpful in order to figure out which direction to take, as there are many ways of doing things in C a lot of the time it seems.
11-23-2003
vandalay

Sorry about that. I have to input a character from the keyboard and test it against the functions in the character handling library. I have all of the functions working, except the ones requiring a string (\n, \t, \r, and such). In those, the only thing recognized is \. I've tried everything I can think of, which isnt a whole lot. Thanks for your patience and help.
11-23-2003
quzah

Code:

int main( void ) { int *character; /* Initializes character */ printf( "Enter a character: "); /* Asks for character and inputs it */ *character = getchar();

This is entirely wrong. You should not be using a pointer here. getchar returns a character, not a pointer to a character. Furthermore, since you are using a pointer, and you aren't actually making it point to something, it points to some random space in memory.

What happens is that as soon as you call getchar the way you are, it overwrites that random spot in memory with whatever getchar returns. This is a BadThing(TM).

Don't use a pointer. Nothing here requires a pointer.

Quzah.
11-24-2003
kermit

Oh crap

Thanks for the correction Quzah

I was actually experimenting, and I am not altogether clear on pointers yet, obviously. What I had wanted to do originally was to make the variable 'character' an array like this:

Code:

int main( void ) { int character[10]; /* Initializes character */ printf( "Enter a character: "); /* Asks for character and inputs it */ character = getchar();

I cannot remember what happened when I tried that - something about a cast - anyway, I was mistaken when I thought that

int character[10];

is the same as

int *character;

Now is it correct to say that the array

Code:

int character[10];

would be ok to use, as there is space set aside for it? This would not over write another part or memory, or would it?
03-29-2004
tzuchan

Quote:

Originally Posted by vandalay

Sorry about that. I have to input a character from the keyboard and test it against the functions in the character handling library. I have all of the functions working, except the ones requiring a string (\n, \t, \r, and such). In those, the only thing recognized is \. I've tried everything I can think of, which isnt a whole lot. Thanks for your patience and help.

Err... Let me point out to you that in order to catch \r and \n, you'd have to use two different functions...

As far as I know, you can only get '\r' when you are using the getch() function (which is in the conio.h, and may be none standard...) and when you press enter.

getchar(), on the other hand, will return '\n' when you press enter.

I haven't tried it out myself, but would assume that in order to return '\t', you'd have to press the "tab" button, not type in \t.
03-29-2004
tzuchan

[QUOTE=kermit]

Code:

int main( void ) { int character[10]; /* Initializes character */ printf( "Enter a character: "); /* Asks for character and inputs it */ character = getchar(); // Err... you're trying to change the address of the array here...

This won't work either...

Your confusion regarding arrays and pointers may caome from the fact that the character (without the square brackets and number) actually refers to the address at which the array is stored. character[i] however, would then refer to the ith element of the character array.

However, in any case, Quzah is correct in the sense that you don't need arrays for what this program has to do in the first place.

This code is an example showing how you can use a pointer to store the address of an array, as well as how to access a particular element in the array through a pointer.

Code:

int main(void) { int character[10], *pointer; pointer = character; pointer[0] = 5; printf("%d", character[0]); return 0; }
03-29-2004
kermit

Quote:

Originally Posted by tzuchan

Your confusion regarding arrays and pointers may caome from the fact that the character (without the square brackets and number) actually refers to the address at which the array is stored. character[i] however, would then refer to the ith element of the character array.

If you have an array called character, something like this:

Code:

char character[10]; char *p; p = character;

Writing character and assigning it to p (as I did above) is not assigning the whole array as you pointed out. No doubt you meant that

Code:

p = character; /* is the same as */ p = &character[0];

When you use the name of the array without the brackets, it is only the address of the first element, not the entire array.

Quote:

Originally Posted by tzuchan

However, in any case, Quzah is correct in the sense that you don't need arrays for what this program has to do in the first place.

Actually Quzah never mentioned that there was no need for arrays. He did say there was no place for pointers. Pointers and arrays are not the same thing. Furthermore, if you read the entire post, you will note that vandalay stated he needed to work with strings - heck I will quote him for you....

Quote:

Originally Posted by vandaly

Any ideas on how I can get the program to take whitespace characters and test them as well? I'm able to enter and check single characters, but it needs to check short strings also.

How do you hold a string without an array?

The only other thing I am wondering is why are you dredging up a 4 month old post? That usually is frowned upon on this board.

~/

[edit]
As an aside, I appreciate your attempt to clear this up for me, though I have learned a bit about arrays and their relationship to pointers in the past four months, and I definitely would not write code such as I did at that time.
[/edit]