Thread: Problems reading in character

Hi,

I just took up c programming and like it so far. Now I got a problem reading in a character in a program. The program looks like this:


insert

Code:

#include <stdio.h>

main()
{
    char c1, c2;
    printf("Letter 1: ");
    c1 = getchar();
    
    printf("Letter 2: \n");
    c2 = getchar();
    
    printf("c1 %c, c2 %c", c1, c2);
    if (c1 < c2)
        printf("Letter 1 is before Letter 2.\n");
    else
        printf("Letter 1 is after Letter 2\n");
}

The program reads in c1, but ignores c2. Anyone knows why?
I have the same problem using scanf (see below).


insert

Code:

#include <stdio.h>

main()
{
    char c1, c2;
    
    printf("Letter 1: ");
    scanf("%c", &c1);
    
    printf("Letter 2: ");
    scanf("%c", &c2);
    
    printf("\nc1 %c, c2 %c", c1, c2);
    if (c1 < c2)
        printf("\nLetter 1 is before Letter 2.\n");
    else
        printf("\nLetter 1 is after Letter 2\n");
}

Any help is appreciated. Thank you.

Using scanf with the %c format specifier is equivalent to using getchar*. If you think about what you type, you type a letter (e.g. 'x'), then you hit the enter key. The enter key sends a newline character to the program, so your first getchar gets the 'x', the second one gets the newline ('\n'). Take a look at this link for more info and one way to clear/flush the input buffer up to the newline -- note, fflush(stdin) is NOT the way.

And I would stick with the getchar version, it's a bit clearer, IMO. Note, however that getchar returns an int (see here) -- this is so it can return all possible chars, as well as special values like EOF. Thus you should declare c1 and c2 to be of type int. And if you really wanted to be thorough, you should check both c1 and c2 for EOF before you compare.

* I'm not feeling 100% sure that the two are completely equivalent, so as a caveat, there may be minor differences. But as far as your issue is concerned, they're the same.

I tried a
#include <windows.h>
and
Sleep(2000); // wait 2 seconds

between c1 and c2 input

and found it was unlikely that a character would go in as c1 and "enter" command would go into c2 but I could be wrong. please explain if you can correct me.


Then I found a line from this page very useful that fixed the problem
FAQ > Flush the input buffer - Cprogramming.com

FAQ > Flush the input buffer

Sleeping won't help. The enter character is in the input buffer once you press enter, and it waits there until it is removed by a function like getchar, scanf, fgets, etc.

Originally Posted by 4eric

...and found it was unlikely that a character would go in as c1 and "enter" command would go into c2 but I could be wrong. please explain if you can correct me.

Run this, and follow the instructions:

Code:

#include <stdio.h>

int main(void)
{
    int c1, c2;

    printf("Enter a single letter: ");
    fflush(stdout);

    c1 = getchar();
    c2 = getchar();

    printf("You entered: %c\n",c1);

    if(c2 == '\n')
        printf("c2 contains a newline\n");

    return 0;
}

thank you very much read the posting

Sleeping won't help. The enter character is in the input buffer once you press enter, and it waits there until it is removed by a function like getchar, scanf, fgets, etc.

I am out of this web forum
Goodbye

Thank you all for all help. Appreciated.