Scanf and ordinary characters.

Hello to all. I have some particular questions about scanf and how its works.

Assuming that we have the code :

Code:

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#include<stdio.h>
int main(void)
{
char mychar;
 
printf(" Give a character : ");
scanf("%c" , &mychar);
 
printf(" Your char is : %c" , mychar);
 
return 0;
}

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Assuming that we have the INPUT :

Code:

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Give a character:    <- I pushed ENTER
 Character is:        <- What is here?

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Well , ENTER character have been stored into mychar variable?

On the other hand if I have

Code:

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scanf(" %c" , &mychar);

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If I give ENTER ( '\n') + A (character) scanf will match ENTER with space ordinary into format string of scanf and then will match A with mychar variable (due to %c conversion specification ??)

Thank you in Advance

Mr. Lnx

In the first case (with no leading whitespace in the format string) mychar will have the value '\n' (typically ASCII 10). If you print that out, it gives a newline.

In the second case, the leading whitespace causes any whitespace to be discarded before placing a character in mychar. '\n' is one of the whitespace characters, so will be skipped. If there are multiple whitespace characters pending, all will be discarded, and scanf() will wait until a non-whitespace character is entered.

Well ,yes this explanation is great .

I think white-space characters are equivalent with new line characters in scanf... is it right?

Mr. Lnx

No. A newline character is one of the characters that are categorised as whitespace. The reverse is not true. There are whitespace characters that are not newlines (such as the space character itself, tab characters, etc).

Yes. It was my fault sorry. I mean a new line character (one) is equivalent to a space... and I say that because if we put a space in format string to scanf next to conversion specification like this ->

Code:

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scanf(" %c" , &mychar);

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either give '\n' or space as input and then a character is the same. Scanf will accept your input in both of cases. Ok?

And last question... you said before that scanf discards white space characters.. (since we have included space in format string) I think that first scanf will match one or more white space characters with space in format string and then will discard them... is it right? I have read it in page 46 of KIng's book C programming a modern approach second edition.

Thank you for your time.

Mr. Lnx

Quote:

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Originally Posted by Mr.Lnx

scanf discards white space characters

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That depends on how you use it. The only specifiers that will read a whitespace character are %c and %[], if the set in [] includes whitespace characters (eg., [ \t\n]). For other specifiers, leading whitespace is discarded until a non-whitespace value is found. If that fits the specifier, it is read. If not, it is left in the buffer and scanf() fails.

" %c" is sort of a special case, in that it also discards leading whitespace, even thought those values could be read into a %c.

Quote:

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Originally Posted by grumpy

No. A newline character is one of the characters that are categorised as whitespace. The reverse is not true. There are whitespace characters that are not newlines (such as the space character itself, tab characters, etc).

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hmmm but space and whitespace characters are the same thing. Aren't they?

Well , Finally I understand it :) thank you very much guys.

Scanf is a strong headache sometimes!!!

Have a nice day.

Mr. Lnx

@Mr.lnx for my codeblocks c compiler does gives undefined behaviour when %c specifier is used i think its best to try this %1s and it's going to be best for collecting characters or your " %1s" to skip whitespace characters before input.

Quote:

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Originally Posted by Nyah Check

@Mr.lnx for my codeblocks c compiler does gives undefined behaviour when %c specifier is used i think its best to try this %1s and it's going to be best for collecting characters or your " %1s" to skip whitespace characters before input.

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Thank you. I only wanted to understand how scanf works with ordinary characters in its format string . I am reading the book of King simultaneously :)
On page 46 of C programming a modern approach second edition it is said that scanf reads / matches white space characters from user's input (if input has some of them because it is not necessary) you may mean when you say that scanf discards these white space characters that they don't be printed .