Scanf changing the input in C

Question

I have a fairly basic problem but I can't manage to solve it.

I'm trying to get an input from a user like this :

int main() {
    char coord[2];

    fflush(stdin);
    scanf("%c", coord);
}

When i'm trying this code with printf("%c", coord);, it displays a completely different string from what I typed. For example, if I type "g6", it prints "Ê". I really have no clue why it's happening.

Thanks for helping me !

where is the printing code? why are you trying to store a character into an array ? — muyustan, Apr 11 '20 at 11:08
Use `%s` for strings. For both `scanf` and `printf`. And make sure the array has enough space for the terminating NUL - that is, `"g6"` requires three bytes to store. — kaylum, Apr 11 '20 at 11:09
Rather than editing your question to say that it has been answered, it is standard practice on Stack Overflow to accept one of the answers given (if that answer has actually addressed your issue). I would recommend that you roll back your edit, or somebody may do it for you. — Adrian Mole, Apr 11 '20 at 11:28

score 2 · Answer 1 · answered Apr 11 '20 at 11:10

2

If you want to get string(char array) from user you should do this :

scanf("%s",coord);

%c is for single char

answered Apr 11 '20 at 11:10

Seyed Mohammad Amin Atyabi

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`scanf("%s",coord);` is as bad a [`gets()`](https://stackoverflow.com/questions/1694036/why-is-the-gets-function-so-dangerous-that-it-should-not-be-used). – chux - Reinstate Monica Apr 11 '20 at 11:21

score 2 · Answer 2 · answered Apr 11 '20 at 11:15

First of all avoid using fflush (stdin);. Standard input flashing is undefined behavior, according to C standard, and may lead to big issues .

Then, you are trying to get an input string using %c format, that is supposed to acquire a single character. Furthermore, your coord array has not enough room for the string terminator character (\0).

The format to be used in order to acquire a string with scanf (and to print it with printf) is %s:

int main() {
    char coord[3] = {0};

    scanf("%2s", coord);

    printf ("%s\n", coord);
}

The "2" added to the format makes sure that at most two characters are read (exactly those you can have in you string array without overwriting the last character).

Vlad from Moscow · Answer 3 · 2020-04-11T11:18:23.750

For starters this statement

fflush(stdin);

has undefined behavior and shall be removed.

The conversion specifier %c of printf expects an argument of the type char while you are passing an expression of the type char * to which the array designator is implicitly converted

printf("%c", coord);

you have to write either

printf("%c", *coord);

or

printf("%c", coord[0]);

Pay attention to that using this call of scanf

scanf("%c", coord);

you can enter only a single character. You can not enter a string.

If you want to enter a string in the array coord that has only two elements then you have to write

scanf( "%1s", coord);

In this case the array will be filled with a string of length equal to 1.

In this case you can output it like

printf("%s", coord);

If you want to enter a string like this "g6" then you have to declare the array like

char coord[3];

and write the following call of scanf

scanf( "%2s", coord);

Adrian Mole · Answer 4 · 2020-04-11T11:23:47.630

The line char coord[2]; declares coord as an array of characters (also known as a "string"). However, the %c (in both scanf and printf) reads/writes a single character.

For strings, you need to use the %s format.

Also, if you want to store/read/print the string, "g6", you will need to allocate (at least) three characters to your coord array, as you must terminate all C-strings with a nul character.

Furthermore, calling fflush on the stdin stream is not effective (actually, it causes undefined behaviour, so anything could happen) - see here: I am not able to flush stdin.

So, a 'quick fix' for your code would be something like this:

#include <stdio.h>
int main()
{
    char coord[3]; // Allow space for nul-terminator
//    fflush(stdin); // don't do it
    scanf("%2s", coord); // The "2" limits input to 2 characters
    printf("%s\n", coord);
    return 0; // ALways good practice to return zero (success) from main
}

Scanf changing the input in C

4 Answers4