How to use Switch from within a loop?

[Tiranasta]

Ok, I have switch (random) within a for loop. The problem is, when I use 'break' to prevent the case falling through, it also stops the loop. Is there a way to prevent this?

[rogerborg]

Please post your code.

[shogun]

You could just use "if (val == 1) ... else if (val == 2) ... else if (val == 3) ... else ..." instead of "switch(val) { case 1: ... break; case 2: ... break; case 3: ... break; default: ... break; }".

[zeno60]

Ok, I have switch (random) within a for loop. The problem is, when I use 'break' to prevent the case falling through, it also stops the loop. Is there a way to prevent this?

I'm pretty sure the break statement only exits out of its enclosing for/while/do loop or switch statement. You must have something else going on for the loop to be ending prematurely.

[MasterGod]

Please post the whole loop code in here.

[Pörzi]

I'm pretty sure the break statement only exits out of its enclosing for/while/do loop or switch statement. You must have something else going on for the loop to be ending prematurely.

I think so too. This proves it.

Code: Select all

#include <iostream>
using namespace::std;

int main()
{
int a=0;

for (0;a<10;a++)
{
	switch (a)
	{
		case 0: break;
		case 1: break;
		default : break;
	}
}

cout << "a = " << a << "\n";

return 0;
}

--> a = 10

[vitek]

No, this proves that the loop executed 10 times. If you got 'a = 0' then you'd be right.

Travis

[Halifax]

No, this proves that the loop executed 10 times. If you got 'a = 0' then you'd be right.

Travis

Exactly, he was trying to prove that it executed 10 times, and did not exit the for loop. It just exited the brackets that it was contained in.

Either way that it how break is supposed to work.

[MasterGod]

Ok, I have switch (random) within a for loop. The problem is, when I use 'break' to prevent the case falling through, it also stops the loop. Is there a way to prevent this?

It doesn't stop the loop..
You even said it yourself, it prints "a = 10" meaning the loop reached the point where it checks "10 < 10 ?" - which is the end of the loop.

[Acki]

@MasterGod: you're talking about 2 different people...

[Daaark]

Code: Select all

#include <iostream>
using namespace::std;

int main()
{
int a=0;

for (0;a<10;a++)
{
	switch (a)
	{
		case 0: goto loopend;
		case 1: goto loopend;
		default : break;
	}
}

loopend:

cout << "a = " << a << "\n";

return 0;
}

This will work fine, and is perfectly okay, despite what some very uptight people may tell you.

[vitek]

Yes, most programmers will say that code is bad because it uses goto. This alone doesn't really bad, but it is easy to write goto code that becomes difficult to follow. Especially since there are other ways to do the same thing that are easier on the eyes. I mean you could implement a for loop using goto, but you don't see people doing that anymore. It's just to hard to follow when the code gets complicated.

The example is pretty convoluted though. The loop and switch would be completely optimized out because the first case bails out of the loop without any side effects.

Travis

[MasterGod]

@MasterGod: you're talking about 2 different people...

The hour did its thing..

About the goto, its low programming, IMO you should look for any other way then using goto.

[Saturn]

Goto has its uses and is sometimes the most elegant solution for a problem. But the example code provided is bad in itself.
Loop-switch over a constant range is something very commonly seen, but mostly it is useless. The code is then better readable if the switch's case statements are just executed in order.

See http://en.wikipedia.org/wiki/Loop-switch_sequence

[Pörzi]

I uploaded an avatar to prevent further confusion.

This will work fine, and is perfectly okay, despite what some very uptight people may tell you.

Imo there are two reasons why one should not use goto:

1) It is generally not regarded as a good way to program.
2) The code will not be easy to read if you use is a lot.