Reading a single character in C

Question

I'm trying to read a character from the console (inside a while loop). But it reads more than once.

Input:

Output:

char : a  char : char : '

Code:

while(..)
{
    char in;
    scanf("%c",&in);
}

How can i read only 'a'?

P.P · Accepted Answer · 2013-01-19T23:51:19.040

40

scanf("%c",&in);

leaves a newline which is consumed in the next iteration.

Change it to:

scanf(" %c",&in); // Notice the whitespace in the format string

which tells scanf to ignore whitespaces.

OR

scanf(" %c",&in);
getchar(); // To consume the newline

edited Jan 19 '13 at 23:51

answered Jan 19 '13 at 23:20

P.P

Actually I want to create a char array.Do have an idea about it? (Input size is uncertain).Thanks! – g3d Jan 19 '13 at 23:36
@vkeles: 1) Allocate an array with some initial size, say `n` using `malloc` 2) Read chars into the array until the it doesn't exceed `n` 3) If `n` chars are read and you want to read more than double the size of the array using `realloc`. This method is generally followed to avoid calling realloc too frequently. Otherwise, you may do the realloc with your preferred size. – P.P Jan 19 '13 at 23:48

score 6 · Answer 2 · answered Jan 19 '13 at 23:29

6

To read just one char, use getchar instead:

int c = getchar();
if (c != EOF)
  printf("%c\n", c);

answered Jan 19 '13 at 23:29

Douglas

score 3 · Answer 3 · edited Apr 03 '21 at 09:12

3

in scanf("%c",&in); you could add a newline character \n after %c in order to absorb the extra characters

scanf("%c\n",&in);

edited Apr 03 '21 at 09:12

Rudolf Adamkovič

answered Jan 20 '13 at 09:15

Manolis Ragkousis

I could not get scanf("%c\n", &in); to work properly. This does work however: scanf(" %[^\n]%*c", &in); The %*c tells scanf to read and discard anything left in the input buffer including newlines. It is always good practice to include a space right after the first " used in scanf. But if you want to preserve the white entered by the user (e.g. spaces before other text is entered), then omit the space following the first " in scanf(). – RobK Jul 16 '21 at 15:59

score 0 · Answer 4 · answered Jan 04 '20 at 09:16

0

you could always use char a = fgetc (stdin);. Unconventional, but works just like getchar().

answered Jan 04 '20 at 09:16

umsee

score -1 · Answer 5 · answered Jan 20 '13 at 03:02

-1

you can do like this.

char *ar;
int i=0;
char c;
while((c=getchar()!=EOF)
   ar[i++]=c;
ar[i]='\0';

in this way ,you create a string,but actually it's a char array.

answered Jan 20 '13 at 03:02

Cocoo Wang

Note that this example doesn't allocate any memory for the character array, nor does it set the initial value of ar, so it will write to an effectively random location in memory, overwriting whatever is there. – Douglas Jan 20 '13 at 10:27
Thank you.I really forget to keep the habit to initialize a pointer variable – Cocoo Wang Jan 20 '13 at 16:40

5 Answers5