Skipping lines of code in C i/o

Question

When learning C in simple programs it often happens that the computer skips the execution of some lines of code, and I can't understand why this is so.

Now as an example, I sketched a program which simply stores 3 numbers entered by the user:

#include <stdio.h>

int main(void)
{
int a, b, c;

printf("Please type in number a: \n");
scanf("%i", &a);
printf("Please type in number c: \n");
scanf("%i", &c);
printf("Please type in number b: \n");
scanf("%i", &b);    
return 0;
}

I want to enter 1, 2, and 3. This is what I get in the console (in Ubuntu):

Please type in number a:
1
Please type in number b:
Please type in number c:
2

The input of number b was ignored.

Not only the second input is skipped, so even the input is in the wrong order. Initially, I wrote everything in alphabetic order in the code - a, b and c, then the input of b was skipped, and then I changed the order in the code and still, as you can see, the execution remained unchanged.

And such cases I have had earlier.

Why is this happening?

Try `scanf("%i%*c", &a);` (for all) as `%*c` would read `'\n'` from stdin and discard it. — ameyCU, Apr 15 '17 at 15:14
@AbrahamLincoln It does as I see . Example [here](https://ideone.com/NoriMp). — ameyCU, Apr 15 '17 at 15:19
@ameyCU I tried this and I also added `printf("%i %i %i\n", a, b, c);` before `return`. Printf was ignored by the program. — Abraham Lincoln, Apr 15 '17 at 15:27
Idea: 1) Code you are compiling and code you are running is not the same. 2) Compiler/option are faulty. 3) Post _exactly_ the keys used as input like `1`, ``,`2`, ``,`3`, `` 4) Printf the return value of each `scanf()`. `int y = scanf("%i", &a); printf("y:%d\n", a);` — chux - Reinstate Monica, Apr 15 '17 at 16:10
What compiler are you using. I tried your code on Cygwin and it works fine? — Gnqz, Apr 15 '17 at 16:12
It could be as simple as the code you edit is not properly saved and _successfully_ compiled before running the executable - IOWs you are running the old code. — chux - Reinstate Monica, Apr 15 '17 at 16:14
The code shown inputs a, c, b in that order; the sample run claims to input them in the conventional order a, b, c. There's a mismatch between what you show. — Jonathan Leffler, Apr 15 '17 at 16:22
@AbrahamLincoln Are you compiling your code after you make the edits? Seems like you are only saving and running the old binary. — Ajay Brahmakshatriya, Apr 15 '17 at 16:28

score 0 · Answer 1 · edited May 23 '17 at 10:31

0

On 2nd thought, I think OP has another issue

Leaving below as community wiki as a reference

To insure output occurs before scanf(), flush the output.

printf("Please type in number a: \n");
fflush(stdout);
scanf("%i", &a);

printf("Please type in number c: \n");
fflush(stdout);
scanf("%i", &c);

See What are the rules of automatic flushing stdout buffer in C?

edited May 23 '17 at 10:31

Community

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answered Apr 15 '17 at 15:26

chux - Reinstate Monica

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I tried `fflush` and the result remains the same I described in the question. – Abraham Lincoln Apr 15 '17 at 15:34

Skipping lines of code in C i/o

1 Answers1