Programming

Hi,

If I have the following code :

int i=2;
switch(i)
{
case 1 : {};break;
default : { printf("d"); };break;
case 2 : { printf("2"); };break;
}


what will be the output?

I had an understanding that case statements are taken sequentially so default will be executed. But when I tried this program it is printing 2.

Can you please help me with this??

default comes when the i does not match any of the specified values given in the cases that is 1 and/or 2

Regards
JK

A modern compiler may be better than an older one when interpreting your code.

Also a different C compiler may compile your code differently than the one you are using.

If you mention your OS and compiler maybe some others could try your code out on in a different environment to see if you there is another answer.

In HP-UX 10.20 C the answer displayed is 2.

I would say that missing the 'break' in a C switch statement is employing a feature of the compiler, not the language. Even though I have used it myself in the past it could lead to problems in the future if the complier or OS was changed.

A similar trick in C is something like

if (flag)
{
/* do some stuff */
}

Here you are relying on the compiler to interpret the variable in a certain way. With compilers nothing is guaranteed and syntax like that in C could just as easily not work the way that you wan it to. Better to say exactly what you mean rather than imply:

if (flag == 1)
{
/* do some stuff */
}

C is a very powerful language precisely because it will almost let you get away with anything. Just as long as the syntax looks ok a compiler will produce any old executable. But it might not work though.

Remember YOU are the one doing the thinking, not the compiler

MBB

I guess all the options are read at once and default is only used as a last option. Is there some reason you want "default" to execute, soorajmu, instead of the correct option?

I must disagree with mbb. The C language is governed by an ansi standard.

Any compiler that takes soorajmu's code and fails to print "2" is broken. Similiarly, code like:
if(flag)
is explicitly allowed and even encouraged. Every compiler must work with code like that.

The order of the cases in a switch only affect fallthroughs and nothing else. mbb doesn't like fallthroughs and many folks agree. Even K&R cautions against them. But fallthroughs are allowed by the standard.

Fallthroughs also violate the tenets of structured programming. I normally adhere to those tenets with a rigidity that most programmers see as unnatural. For instance, I never have used setjmp/longjmp and I never will. But I actually like fallthroughs. I believe that they can result in more readable code than is possible with pure structured techniques. For example, I like this kind of thing:

Code:

switch(i)
{
      case 1:   function1();
                break;
      default:  printf("Illegal value, defaulting to 2\n"); 
      case 2:   function2();
                break;
}

Now, that is just example code. With only a single call to function2(), I might just duplicate it in the default case and not fallthrough to case 2. But imagine more lines of code. If I duplicate them all, a programmer must compare them to be sure that the default case and the 2 case are exactly the same.

Perderabo has a fair point. A feature of the language then, and the C language is governed by standards.

Even so, standards may change and compilers have been known to have faults ...

Exploiting C's loose typing could cause you more problems that it would solve. If you code fall throughs, undefined conditionals, undefined type casting etc then you leave the door wide open for unpredicatable and/or faulty code.

(The HP 11.00 C compiler is stricter than the HP 10.20 C compiler and traps problems with loose typing that used pass through)

Anyway, just trying to highlight some of the pitfalls with C.