Thread: All combinations

visit, do more and incr are just line labels.

You need to include them! I'm not familiar with the code itself, but try using the whole thing.

Check what your compiler needs for line labels though. I know in Turbo C, it required a semi-colon on the line immediately following the label:

Code:

visit:
;

Your HD will be much more the bottleneck, AFTER you have filled up it's cache memory, not before.

well, I did include them all as is, but i get this error:

Code:

test.C:6: error: `main' must return `int'
test.C: In function `int main(...)':
test.C:10: error: invalid conversion from `void*' to `int*'
test.C:44:2: warning: no newline at end of file

If i change the main to int and return 0(code below) I get this error

Code:

test.C: In function `int main()':
test.C:10: error: invalid conversion from `void*' to `int*'
test.C:41:2: warning: no newline at end of file

Changed main to int version:

Code:

#include <stdio.h>
#include <stdlib.h> 


int main()
{
	int i, j=1, k, n, *c, x;
	printf( "Enter n,k: ");
	scanf( "%d,%d", &n, &k);
	c = malloc( (k+3) * sizeof(int));
 
	for (i=1; i <= k; i++)
	{
		c[i] = i;
		c[k+1] = n+1;
		c[k+2] = 0;
		j = k;
	}

visit:
	for (i=k; i >= 1; i--) printf( "%3d", c[i]);
	printf( "\n");
	if (j > 0) {x = j+1; goto incr;}
	if (c[1] + 1 < c[2])
	{
		c[1] += 1;
		goto visit;
	}

	j = 2;

do_more:
	c[j-1] = j-1;
	x = c[j] + 1;
	if (x == c[j+1]) {j++; goto do_more;}
	if (j > k) exit(0);

incr:
	c[j] = x;
	j--;
	goto visit;

return(0);
}

Remove the comma from inside the scanf() format string. Just enter the numbers as:

number1 number2

with no comma there, as you enter.

I haven't run this program, but that code looks like it kicks some serious buttinski! Leave it to Knuth!

So you correct the code to int main and return 0 and then what? Uncomment everything, try to compile it and then post the errors you are getting.

I doubt anybody cares what ridiculous lengths you have to go to to get Turbo Crap to work as we don't advocate using such obscenely out of date nonsense.

Edit: Damn, crossed posts.

That error on line 10 is because you're compiling this as C++ code, which requires a cast from void * to any other type. C does not require a cast from void * to other pointer types, and in fact, casting malloc is not recommended in C code (read this: Cprogramming.com FAQ > Casting malloc).

Also, that code you uncommented, while it may work, looks pretty crappy. It uses goto, which is generally considered bad practice (read: Goto Considered Harmful). Also, it uses a bunch of variable names that make no sense and it's totally uncommented, so it's hard to say what it really does.

If you want combinations where order doesn't matter and there are no repeats, and you always want combinations of 5 elements, then you can hack it with a bunch of nested for loops:

Code:

#define N_ELEMENTS    13
char *elements[N_ELEMENTS] = {"H", "B", "C", "N", "P", "O", "S", "Se", "F", "Cl", "Br", "I", "F"};
int a, b, c, d, e;

for (a = 0; a < N_ELEMENTS - 5; a++) {
    for (b = a + 1; b < N_ELEMENTS - 4; b++) {
        ...
                for (e = d + 1; e < N_ELEMENTS; e++) {
                    printf("%s %s %s %s %s\n", elements[a], elements[b], ..., elements[e]);
                }
    }
}

Note, that's untested, but should give you the general idea.

Here is the code with basically a direct translation to remove the gotos:

Code:

#include <stdio.h>
#include <stdlib.h>

int main(void)
{
    int i, j=1, k, n, *c, x;
    printf("Enter n,k: ");
    scanf("%d,%d", &n, &k);
    c = malloc((k+3) * sizeof(int));

    for (i=1; i <= k; i++)
    {
        c[i] = i;
        c[k+1] = n+1;
        c[k+2] = 0;
        j = k;
    }

    for (;; j--)
    {
        for (i=k; i >= 1; i--)
            printf("%3d", c[i]);
        printf("\n");

        if (j > 0)
            x = j+1;
        else
        {
            if (c[1] + 1 < c[2])
            {
                c[1] += 1;
                continue;
            }

            for (j=2; ; j++)
            {
                c[j-1] = j-1;
                x = c[j] + 1;
                if (x != c[j+1])
                    break;
            }
            if (j > k)
                break;
        }

        c[j] = x;
    }

    return 0;
}

Removing them is not really that hard, and certainly improves the readability of the flow of the code. Although as you can see the code is still very strange looking anyway.

Originally Posted by iMalc

Here is the code with basically a direct translation to remove the gotos:

Code:

...
                c[1] += 1;
                continue; /* basically a goto */
            }
            /* could be an else block instead of that continue */
            /* which is also basically a goto... */
            for (j=2; ; j++)
            {
                c[j-1] = j-1;
                x = c[j] + 1;
                if (x != c[j+1])
                    break; /* pretty much a goto */
...
    return 0; /* also basically a goto :P */
}

It's funny that everyone complains about goto, since most control statements are basically the same thing as goto.


Quzah.

Originally Posted by quzah

It's funny that everyone complains about goto, since most control statements are basically the same thing as goto.

Fine, conveniently ignore all the things that break, else, and continue can't do that goto can, and instead focus on the one thing that they can all do. Surely, all the most convincing scientific studies also conveniently throw away half of the data.

Okay so I missed an opportunity to use an else instead of a continue. One point is that I made it possible to see such an opportunity.

But really... a return is "also basically a goto". Dream on!

Originally Posted by iMalc

Fine, conveniently ignore all the things that break, else, and continue can't do that goto can, and instead focus on the one thing that they can all do. Surely, all the most convincing scientific studies also conveniently throw away half of the data.

It wasn't sniping at you, I was pointing out that a continue is just a goto. All you are doing is jumping from where you are, to another point. People always say goto is bad because it makes the code hard to follow. Well, a continue does the same thing. It short circuits the flow of the loop and jumps back to the start.

Originally Posted by iMalc

But really... a return is "also basically a goto". Dream on!

Of course it is. You are jumping from the middle of one function back to another. Conceptually they are identical, except for the part where return can also bring along a value with it.

The concept of jumping around from one point to another is what I was drawing parallels with. A goto and a return leap from wherever you are, to another spot in the code. The only difference is that returns can only jump backwards.


Quzah.