what is the purpose of putting a space in scanf like this scanf(“ %c”,&ch) in place of scanf(“%c”,&ch)? [duplicate]

Answer 1

what is the purpose of putting a space in scanf like this scanf(" %c",&ch) in place of scanf("%c",&ch)?

So that scanf would ignore all spaces before the first non-space character is encountered in the stream.

Also what is input buffer in fflush(stdin)?

What you input into the console will exist in the stdin stream.

Don't flush that stream however, it's undefined behavior. If you want to discard characters entered after scanf is called, you can read and discard them.

Answer 2

Because the space before %c ignores all whitespace. *scanf family of functions ignore all whitespace before any % by default except for %c, %[ and %n. This is mentioned in C11 at:

7.21.6.2.8

Input white-space characters (as specified by the isspace function) are skipped, unless the specification includes a [, c, or n specifier.

To be complete, here's the part that says all whitespace will be ignored:

7.21.6.2.5

A directive composed of white-space character(s) is executed by reading input up to the first non-white-space character (which remains unread), or until no more characters can be read. The directive never fails.

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Regarding your second question, fflush(stdin) causes undefined behavior and must not be used (emphasis mine):

7.21.5.2.2

If stream points to an output stream or an update stream in which the most recent operation was not input, the fflush function causes any unwritten data for that stream to be delivered to the host environment to be written to the file; otherwise, the behavior is undefined.

Answer 3

The space in the scanf in this case tells scanf to ignore any leading whitespace characters in front of the character you read. Still even if there is no whitespace in front of the character the code will work and read the character successfully.

I am not sure what you are asking in your last question, but stdin is the standard input stream for you program.

Answer 4

Just to give a space from the last object, if not, for example a string, everything will be together with no spaces between them.

Answer 5

scanf(" %c",&ch);

As per the man page,

White space (such as blanks, tabs, or newlines) in the format string match any amount of white space, including none, in the input.

Stdin is standard input.The user enters the data for the program, this is first stored in a buffer and then when the program requests data transfers by use of the read operation the data is made available to the program. (using scanf etc).

Answer 6

I had the same problem a while ago in which if I would try to read a variable using scanf ("%c", &ans); it would not read anything. Thus I figured out that the \n character from the last input was being read.

Thus, doing scanf (" %c", &ans); solved my problem.

Although, I could not understand your second question clearly.