What compiler is doing when we pass unnecessary parameters in scanf

What compiler is doing when we pass unnecessary parameters in scanf

[RAM_LOCK]

Hi,
In the second scenario what value is it printing when i have given extra
parameter in scanf?
Does it vary from compiler to compiler?

Scenario : I
-------------
root@kaushik_Fedora11 ~/C/LET_US_C/ch-1> cat simple-interest.c
#include <stdio.h>

void main ()
{
        int p;
        float i=0;
        printf ("enter the principal amount\n");
        scanf ("%d",&p);
        i = (p*5*5)/100;
        printf ("Interterest is : %f\n",i);
}
root@kaushik_Fedora11 ~/C/LET_US_C/ch-1> ./a.out
enter the principal amount
100
Interterest is : 25.000000


Scenario : II
-------------
> cat simple-interest.c
#include <stdio.h>

void main ()
{
        int p;
        float i=0;
        printf ("enter the principal amount\n");
        scanf ("p:%d",&p);
        i = (p*5*5)/100;
        printf ("Interterest is : %f\n",i);
}
root@kaushik_Fedora11 ~/C/LET_US_C/ch-1> ./a.out
enter the principal amount
100
Interterest is : -9321198.000000

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Fwd: What compiler is doing when we pass unnecessary parameters in scanf

[Aneesh Bhasin]

----forgot to add list as cc------

Hi Kaushik,

any extra non-whitespace, non "%" characters are matched against the
input given from stdin - if they match, it is ignored and if it
doesn't match, no further input is taken.

In case of your second scenario, when you specify "p:%d" as string,
the program expects the input to be of the format "p:<some number>"
but since you give 100 as the input, no value is assigned to the
variable p (you can check the return value of scanf - its zero) and
hence, whatever junk value is in variable p, it is used for further
calculation.

With the second scenario, try giving the input as "p:100" and then p
should get value 100 as expected...

Hope that helps.
Aneesh

On Wed, Jul 29, 2009 at 7:48 PM, RAM_LOCK <Kaushik.Sarkar@netapp.com> wrote:
>
> Hi,
> In the second scenario what value is it printing when i have given extra
> parameter in scanf?
> Does it vary from compiler to compiler?
>
> Scenario : I
> -------------
> root@kaushik_Fedora11 ~/C/LET_US_C/ch-1> cat simple-interest.c
> #include <stdio.h>
>
> void main ()
> {
>        int p;
>        float i=0;
>        printf ("enter the principal amount\n");
>        scanf ("%d",&p);
>        i = (p*5*5)/100;
>        printf ("Interterest is : %f\n",i);
> }
> root@kaushik_Fedora11 ~/C/LET_US_C/ch-1> ./a.out
> enter the principal amount
> 100
> Interterest is : 25.000000
>
>
> Scenario : II
> -------------
> > cat simple-interest.c
> #include <stdio.h>
>
> void main ()
> {
>        int p;
>        float i=0;
>        printf ("enter the principal amount\n");
>        scanf ("p:%d",&p);
>        i = (p*5*5)/100;
>        printf ("Interterest is : %f\n",i);
> }
> root@kaushik_Fedora11 ~/C/LET_US_C/ch-1> ./a.out
> enter the principal amount
> 100
> Interterest is : -9321198.000000
>
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> Sent from the linux-c-programming mailing list archive at Nabble.com.
>
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Re: What compiler is doing when we pass unnecessary parameters in scanf

[Glynn Clements]

RAM_LOCK wrote:

> In the second scenario what value is it printing when i have given extra
> parameter in scanf?
> Does it vary from compiler to compiler?

>         scanf ("p:%d",&p);
>         i = (p*5*5)/100;
>         printf ("Interterest is : %f\n",i);
> }
> root@kaushik_Fedora11 ~/C/LET_US_C/ch-1> ./a.out
> enter the principal amount
> 100
> Interterest is : -9321198.000000

The p: isn't matched in the input, so scanf() skips the following %d
conversion, leaving p unchanged. So p will contain garbage (i.e. 
whatever value happened to be stored in that memory location already).

-- 
Glynn Clements <glynn@gclements.plus.com>

Re: What compiler is doing when we pass unnecessary parameters in scanf

[shiva kumar]

behavior of this is undefined just do man scanf

RAM_LOCK wrote:
> 
> Hi,
> In the second scenario what value is it printing when i have given extra
> parameter in scanf?
> Does it vary from compiler to compiler?
> 
> Scenario : I
> -------------
> root@kaushik_Fedora11 ~/C/LET_US_C/ch-1> cat simple-interest.c
> #include <stdio.h>
> 
> void main ()
> {
>         int p;
>         float i=0;
>         printf ("enter the principal amount\n");
>         scanf ("%d",&p);
>         i = (p*5*5)/100;
>         printf ("Interterest is : %f\n",i);
> }
> root@kaushik_Fedora11 ~/C/LET_US_C/ch-1> ./a.out
> enter the principal amount
> 100
> Interterest is : 25.000000
> 
> 
> Scenario : II
> -------------
>> cat simple-interest.c
> #include <stdio.h>
> 
> void main ()
> {
>         int p;
>         float i=0;
>         printf ("enter the principal amount\n");
>         scanf ("p:%d",&p);
>         i = (p*5*5)/100;
>         printf ("Interterest is : %f\n",i);
> }
> root@kaushik_Fedora11 ~/C/LET_US_C/ch-1> ./a.out
> enter the principal amount
> 100
> Interterest is : -9321198.000000
> 
> 

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