How would I only let the user input one character in c - c

Question

If I only want the user to enter one char, how would I go about doing that in the c language. My attempt at this is below but it failed horribly. From what i read online I heard you could use the function gets or fgets to accomplish this, but I could not figure out how.
do
{
geussNumber += 1;
printf("Enter guess number %d\n", geussNumber);
scanf(" %c", &geussLetter);
scanf ("%c", &inputViolation);
if (isalpha(geussLetter) == 0)
{
printf("You did not enter a letter\n");
}
else if (inputViolation == true)
{
printf("You eneterd more than one letter\n");
}
else
{
inputLoopEnd = 1;
}
}
while( inputLoopEnd == false );

Answer 1

You could use the getc family of functions.
Have a look at http://quiz.geeksforgeeks.org/difference-getchar-getch-getc-getche/ for example.

Answer 2

It seems you want to read input one line at a time (i.e. the user types a one-letter guess and then <enter>), and you want to verify that the guess indeed contains only a single letter. Couching the problem in those terms perhaps makes it clearer how fgets() could be applied, as that function's purpose is to read one line at a time. Having read a whole line -- or at least as much as the buffer can accommodate -- you can validate it and extract the guess.
scanf() is hard to use properly, so I do recommend the fgets() approach. If you insist on using scanf(), however, then you might do it like this:
// consumes leading whitespace, inputs one character, then consumes any
// immediately-following run of spaces and tabs:
int result = scanf(" %c%*[ \t]", &guessLetter);
if (result == EOF) {
// handle end-of-file ...
} else {
assert(result == 1); // optional; requires assert.h
int nextChar = getchar();
if ((nextChar == '\n') || (nextChar == EOF)) {
// handle multiple-character guess ...
} else if (!isalpha(guessLetter)) {
// handle non-alphabetic guess ...
} else {
// it's valid ...
}
}

Answer 3

Do not use things like fgets() or fputs() etc... They are falling out of use.
As you can see from the description here... this function is designed to handle objects of type str, and you are more focused on using chars at the moment so why not just handle only chars to make life easier.
You can't do this the way you think you can...
scanf(" %c", &geussLetter);
scanf ("%c", &inputViolation);
This can't work because even if the user enters in only one char the way they are supposed to, it's still going to trigger your inputViolation scheme.
Edit: 12:14pm 7/20/2016
I really like the elegance of MOHAMAD's solution on the community wiki.
So I edited to fit your situation and it works well here too. Same idea...
#include <stdio.h>
#include <stdlib.h>
int clean_stdin()
{
while (getchar() != '\n');
return 1;
}
int main(void)
{
int first_time_around = 0;
char theguess = 0;
char c;
do
{
if (first_time_around == 0)
first_time_around++;
else
printf("Wrong input \n");
printf("Enter guess number: \n");
} while (((scanf("%c%c", &theguess, &c) != 2 || c != '\n')
&& clean_stdin()) || !isalpha(theguess));
return 0;
}