Why is the following C code asking input twice?

Question

#include<stdio.h>

int main()
{
  int i, j;
  for(scanf("%d ",&i); i<=10; i++)
    printf("%d ",i);
  return 0;
}

I am a beginner in the programming world so please help me understand why on compiling the above C code it asks inputs twice.Maybe there's some logic to loop here I might be missing. Please help me understand.Thanks in advance.:)

So what's with the space?.Why should it prompt me once again for input? Please give reason — shuberman, Sep 10 '17 at 15:55
The space means it will try to read the space, so you're reading a number and a space, not just a number — savram, Sep 10 '17 at 15:56
The space I was giving in scanf was prompting me to take input twice...But still I need an explanation why a space in scanf () would prompt me 2wice for input — shuberman, Sep 10 '17 at 15:57
It does not ask for anything. It just waits for input. That aside it is a good to get familiar with the manual pages — Ed Heal, Sep 10 '17 at 15:58
In the `scanf` format string, the space character skips the space character from the input and waits for non-space characters to be entered. — BLUEPIXY, Sep 10 '17 at 15:58
@EdHeal: Whether "*waiting*" is taken as "*asking*" might be cultural decision, question, issue, ... — alk, Sep 10 '17 at 16:01
Thank you everyonefor such active responses. I appreciate you all for the help....Keep doing the good work — shuberman, Sep 10 '17 at 16:01
Duplicate of "trailing white space in scanf format string is evil", which is related to what the linked question covers, but there are other questions and answers which deal explicitly with trailing white space. — Jonathan Leffler, Sep 10 '17 at 16:42

score 4 · Accepted Answer · answered Sep 10 '17 at 15:55

4

Change this:

scanf("%d ",&i);

to this:

scanf("%d",&i);

Read more in What does space in scanf mean?

answered Sep 10 '17 at 15:55

gsamaras

71,951
46
188
305

2

Thanks ..This is a very common mistake ...Now I know what was happening ...Thank you very much sir ... :) – shuberman Sep 10 '17 at 15:58
@user7841468 Better: don't use scanf at all. Always get input a line at a time (posix `getline`, or implement it yourself as a loop around `fgets`), and *then* parse it (possibly using `sscanf`) – o11c Sep 10 '17 at 17:18

score 0 · Answer 2 · answered Sep 10 '17 at 20:36

0

Currencly, you placed scanf() in a for loop, which it asks for input for a 10 times.This will not happen when you remove scanf() from for loop.

answered Sep 10 '17 at 20:36

filipivanisevic

3
3

`scanf()` is in the initialization part of the `for` loop. It'll only run once. – Arkia Sep 10 '17 at 20:57

score 0 · Answer 3 · answered Jan 25 '21 at 06:05

0

I was facing the same problem and the only change I did was to change "%d " to "%d". This solves the problem.

answered Jan 25 '21 at 06:05

SIDDHARTHA SARKAR

1

Why is the following C code asking input twice?

3 Answers3