Read two characters consecutively using scanf() in C

Question

I am trying to input two characters from the user t number of times. Here is my code :

int main()
{
    int t;
    scanf("%d",&t);
    char a,b;

    for(i=0; i<t; i++)
    {
        printf("enter a: ");
        scanf("%c",&a);

        printf("enter b:");
        scanf("%c",&b);
    }
    return 0;
}

Strangely the output the very first time is:

enter a: 
enter b:

That is, the code doesn't wait for the value of a.

Filipe Gonçalves · Accepted Answer · 2014-06-07T19:59:04.833

10

The problem is that scanf("%d", &t) leaves a newline in the input buffer, which is only consumed by scanf("%c", &a) (and hence a is assigned a newline character). You have to consume the newline with getchar();.

Another approach is to add a space in the scanf() format specifier to ignore leading whitespace characters (this includes newline). Example:

for(i=0; i<t; i++)
{
    printf("enter a: ");
    scanf(" %c",&a);

    printf("enter b: ");
    scanf(" %c",&b);
}

If you prefer using getchar() to consume newlines, you'd have to do something like this:

for(i=0; i<t; i++)
{
    getchar();
    printf("enter a: ");
    scanf("%c",&a);

    getchar();
    printf("enter b:");
    scanf("%c",&b);
 }

I personally consider the former approach superior, because it ignores any arbitrary number of whitespaces, whereas getchar() just consumes one.

edited Jun 07 '14 at 19:59

answered Jun 07 '14 at 17:54

Filipe Gonçalves

20,783
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1

...or you can place a space before `%c` in `scanf`---> `scanf(" %c", &a)`. – haccks Jun 07 '14 at 18:01
1

@haccks Yep, true, I'll add this to my answer - thanks for the tip ;) – Filipe Gonçalves Jun 07 '14 at 18:02
just adding getchar before the loop does not work..however adding getchar just at the beginning of the loop and at the end of loop works in this case. – coder_r Jun 07 '14 at 18:08
@babji Yep, using `getchar()`before the loop only won't work. I realized that, but then edited my answer and forgot to remove this part. Thanks for noting though, I have removed it now. – Filipe Gonçalves Jun 07 '14 at 19:59
@FilipeGonçalves: Thanks, knew something new after reading your wonderful answer. – Destructor Feb 10 '16 at 14:17

score 0 · Answer 2 · answered Jun 07 '14 at 17:56

0

By seeing your code it's perfect it should read T times A and B but it replaces A and B every time the for each loop.

Use array or hash table to store effectively

answered Jun 07 '14 at 17:56

Saiteja prasadam

96
1
8

The question is just about the input, not processing a and b, so you're answering a different question, not this one. – Rob11311 Jun 07 '14 at 17:59
Sorry didn't get ur question hope that helps – Saiteja prasadam Jun 07 '14 at 18:02

score 0 · Answer 3 · answered Jun 07 '14 at 18:01

0

Some formats used with scanf makes a newline trimmed from stdin but others don't. Reading using "%d" falls into latter category. You need to read a newline '\n' before reading into

scanf("%c", &a);

answered Jun 07 '14 at 18:01

4pie0

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Read two characters consecutively using scanf() in C

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