fgets prints out 'à' instead of an actual input - c

Question

I am trying to write a program in C so that it takes input from the user which can only be 'Q' 'q' 'N' 'n' '1' or '2', everything else should be invalid. I am new to C thus I still can't figure out how fgets suppose to work. Whatever i enter as an input comes out as an 'à'.
char C=' ';
int N=0;
int flag=1;
char buffer[20];
char input[20];
printMenu();
printf("\n\nPlease choose something: ");
fgets(buffer, sizeof(buffer), stdin);
sscanf(buffer, "$s",&input);
//checking the input, shows à instead of an actual input
printf("Input is %c\n", input);
if(*input=='C'||*input=='c')
C=userInputChar();
else
if(*input=='N'||*input=='n')
N=userInputInt();
else
if(*input=='1')
printTriangleLeft(C,N);
else
if(*input=='2')
printTriangleRight(C,N);
else
if(input[0]=='Q'||input[0]=='q'){
printf("Exiting the program...");
return 0;
}
else
printf("Invalid input");

Answer 1

You're not checking the return value of sscanf, so you don't know whether it successfully parsed anything.
Your sscanf format string is $s, which doesn't extract any values. The &input argument is ignored. Besides, there is no scanf format that would take an argument of type char (*)[20] anyway.
printf %c takes an int. You're passing it a char *. This is why you're getting garbage output.
*input=='C' doesn't work either because *input is uninitialized at this point.

Answer 2

You should not pass array pointer into sscanf.
array itself is enough and $s is incorrect also. '%s' you should use to get string
Correct is like following:
sscanf(buffer, "%s", input);

Answer 3

Changed the following :
char buffer[20];
char input[20];
printf("\n\nPlease choose something: ");
fgets(buffer, sizeof(buffer), stdin);
sscanf(buffer, "$s",&input);
printf("Input is %c\n", input);
to
char buffer[20];
char input;
fgets(buffer, sizeof(buffer), stdin);
sscanf(buffer, "%c",&input);
printf("Input is %c\n", input);
seems to be working at least for one character

Answer 4

Continuing from my comment, in addition to the various syntax errors you have in your code, you are simply making this harder on yourself than it needs to be. Here, if I understand your question correctly, you want to take input and validate that it is made up of only the characters "Qqn12".
To validate your input is entirely made up on "Qqn12", you need to loop over each character in your input buffer and check that it is one of "Qqn12". If not the input is invalid.
Before we get there, lets talk about the proper way to validate and remove the '\n' included in the buffer filled by fgets (POSIX getline also includes the trailing '\n' in it buffer as well). To remove the trailing newline, you can either use strrchr to locate it, or you can just use strlen to get the length of the buffer and check that buffer[len - 1] == '\n'. If buffer[len - 1] is NOT equal to '\n' then you know character remain unread in stdin (because the number of chars in stdin either equal or exceed buffer size) and you need to handle that error. For example you can use the following:
char buf[MAXC] = "";
size_t len;
printf ("enter string: "); /* prompt, read and validate */
if (!fgets (buf, MAXC, stdin)) {
fprintf (stderr, "error: invalid input or user canceled.\n");
return 1;
}
len = strlen (buf); /* get buf length */
if (len && buf[len-1] == '\n') /* check for '\n' */
buf[--len] = 0; /* overwrite with '\0' */
else { /* input equals or exceeds buffer size, '\n' not read */
fprintf (stderr, "error: input exceed %d chars.\n", MAXC-2);
return 1;
}
(note the test condition len && buf[len-1] == '\n', you must check that len > 0 before testing buf[len-1] == '\n', or Undefined Behavior is invoked by attempting to read a negative array index.)
Next, you want to limit your input to just the chosen characters, so make a string literal containing the characters you will accept, e.g. char *accept = "Qqn12";. string.h provides the strchr function that will locate and return a pointer to the first occurrence of a given character c in a string s. The declaration is:
char *strchr(const char *s, int c);
Obviously, it does no good to look for one of the characters "Qqn12" in your buffer, because there could be other characters not "Qqn12" there too. However, if we turn the search around and ask "Is each character in buffer in accept (e.g. one of "Qqn12")", then you have exactly the test you are looking for -- and strchr does the work of scanning each char in accept for you. For example you could do the following:
...
char *accept = "Qqn12";
...
for (char *p = buf; *p; p++) /* for each char in buf */
if (!strchr (accept, *p)) { /* if not in 'accept', error */
fprintf (stderr, "error: invalid input '%c'.\n", *p);
return 1;
}
If you are more comfortable with array indexing than pointers, you can simply use array indexing to iterate over each character in buffer, e.g. the following does the exact same thing:
for (int i = 0; buf[i]; i++) /* for each char in buf */
if (!strchr (accept, buf[i])) { /* if not in 'accept', error */
fprintf (stderr, "error: invalid input '%c'.\n", buf[i]);
return 1;
}
(you can even use i < len instead of buf[i] for the exit condition if you like)
Putting all the pieces together, you can validate an entry made up of "Qqn12" is entered with something like the following:
#include <stdio.h>
#include <string.h>
#define MAXC 512
int main (void) {
char buf[MAXC] = "",
*accept = "Qqn12";
size_t len;
printf ("enter string: "); /* prompt, read and validate */
if (!fgets (buf, MAXC, stdin)) {
fprintf (stderr, "error: invalid input or user canceled.\n");
return 1;
}
len = strlen (buf); /* get buf length */
if (len && buf[len-1] == '\n') /* check for '\n' */
buf[--len] = 0; /* overwrite with '\0' */
else { /* input equals or exceeds buffer size, '\n' not read */
fprintf (stderr, "error: input exceed %d chars.\n", MAXC-2);
return 1;
}
for (char *p = buf; *p; p++) /* for each char in buf */
if (!strchr (accept, *p)) { /* if not in 'accept', error */
fprintf (stderr, "error: invalid input '%c'.\n", *p);
return 1;
}
printf ("valid input : %s\n", buf);
return 0;
}
Example Use/Output
$ ./bin/validinput
enter string: Qqn12n21Qq
valid input : Qqn12n21Qq
$ ./bin/validinput
enter string: Qqn12n21Qbq
error: invalid input 'b'.
Look things over and let me know if you have any further questions.