Input data in loop

Question

I want to input data by format "%d:%c"

I have this:

#include <stdio.h>

int main() {
    int number;
    char letter;
    int i;

    for(i = 0; i < 3; i ++) {
        scanf("%c:%d", &letter, &number);
        printf("%c:%d\n", letter, number);
    }
}

I expect this:

Input: "a:1"
Output: "a:1"
Input: "b:2"
Output: "b:2"
Input: "c:3"
Output: "c:3"

But my program doing something like this:

a:1
a:1
b:2

:1
b:2

--------------------------------
Process exited with return value 0
Press any key to continue . . .

What is the problem here?

Do you try to add \n in your scanf ?

Jarod42
– Jarod42

2014-01-05 10:59:54 +00:00
Commented Jan 5, 2014 at 10:59 — Jarod42
– Jarod42, Commented Jan 5, 2014 at 10:59

Some programmer dude · Accepted Answer · 2014-01-05 11:00:40Z

6

It's because when you read the input with scanf, the Enter character is still left in the buffer, so your next call to scanf will read it as the character.

This is easily solvable by telling scanf to skip whitespace, by adding a single space in the format code, like

scanf(" %c:%d", &letter, &number);
/*     ^                */
/*     |                */
/* Notice leading space */

answered Jan 5, 2014 at 11:00

Some programmer dude

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Comments

Community · Accepted Answer · 2017-05-23 10:32:20Z

0

this link might be helpful. using of %c after %d in scanf() function leads you in such difficulty.

Explaining in short, the '\n' you input after giving the number input of first test case will be taken as character input of second test case.

to avoid that you can edit your scanf statements as scanf(" %c:%d",...); . A leading space before %c avoids taking all those '\n' inputs as characters.

edited May 23, 2017 at 10:32

CommunityBot

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answered Jan 5, 2014 at 12:31

vinayawsm

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Comments

chux · Accepted Answer · 2014-01-06 03:16:16Z

0

OP says "... input data by format "%d:%c", yet code uses "%c:%d" and data input implies "char" then "number".

Suggest:

1) Determine the order desired.

2) Use a space before "%c" as in " %c" to consume leading whitespace like the previous line's Enter (or '\n').

answered Jan 6, 2014 at 3:16

chux

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