Please give me explanation of this code.

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1.00/5 (1 vote)

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Explain me the second line of code. What will be the output?

What I have tried:

C

#include <stdio.h>
#define scanf "%s me "
int main()
{
  printf(scanf, scanf);
  getchar();
  return 0;
}

Posted 22-Nov-21 19:02pm

poojitha08

Updated 22-Nov-21 20:43pm

CPallini

v2

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3 solutions

Solution 2

#define is part of the C text preprocessor: it does a text replace of the first part with the second part. You can do more with it than that, but that's the general idea - all it ever does is replace text: C Language: #define Directive (macro definition)[^]

So everywhere in your code you write scanf in your code it will be replaced with "%s me "

#define is there to make code more readable:

C

#define true (1==1)
#define false (1==0)
#define strDbConnect "Server=[SqlDev];Database=[Accounts];password=[NONE];user = [ME]"

So you can write stuff like this:

C

while (true)
   {
   OpenSql(strDBConnect);
   ...
   }

And make it easy to read (and safer, because the DB string is only entered once in the whole program).
I agree with KarstenK - the code you show is just stupid nonsense.

Posted 22-Nov-21 20:34pm

OriginalGriff

Solution 1

The second line is dangerous nonense. At first it is wrong and second it substitutes the scanf documentaion and example code.

Best is to visit some Learn C tutorial to learn understand and use the language.

Tip: install some IDE, like Visual Studio.

Posted 22-Nov-21 19:57pm

KarstenK

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CPallini · Accepted Answer · 2021-11-22T20:43:00

The output would be

%s me  me

Because the second line is telling the preprocessor to replace every occurrence of scanf with "%s me", so that the compiler will actually 'see':

C

int main()
{
  printf("%s me ", "%s me");
  getchar();
  return 0;
}

That said, such line, as pointed out by KarstenK, hides the declaration of the C standard I/O function scanf, fscanf, sscanf, scanf_s, fscanf_s, sscanf_s - cppreference.com[^].
No need to say it is something you should avoid (C programs maybe criptic on their own, no need to make them awkward).