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 · 2013-01-19 23:51:19Z

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, 2013 at 23:51

answered Jan 19, 2013 at 23:20

P.P

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2 Comments

g3d Over a year ago

Actually I want to create a char array.Do have an idea about it? (Input size is uncertain).Thanks!

P.P Over a year ago

@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.

Douglas · Accepted Answer · 2013-01-19 23:29:29Z

6

To read just one char, use getchar instead:

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

answered Jan 19, 2013 at 23:29

Douglas

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Comments

Rudolf Adamkovič · Accepted Answer · 2021-04-03 09:12:04Z

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 3, 2021 at 9:12

Rudolf Adamkovič

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answered Jan 20, 2013 at 9:15

Manolis Ragkousis

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1 Comment

RobK Over a year ago

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().

umsee · Accepted Answer · 2020-01-04 09:16:43Z

0

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

answered Jan 4, 2020 at 9:16

umsee

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Comments

Cocoo Wang · Accepted Answer · 2013-01-20 03:02:40Z

-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, 2013 at 3:02

Cocoo Wang

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3 Comments

Douglas Over a year ago

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.

Cocoo Wang Over a year ago

Thank you.I really forget to keep the habit to initialize a pointer variable

user1658543 Over a year ago

There is a ) missing after getchar(). And, as @Douglas already mentioned, char ar* should be something like char ar[100], giving the array a size.

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