Execute a loop x times without loop or if statements

Question

How can I rewrite the following program in order to not use any loop and branch constructs? (No if, while, break, continue, switch, ...)

for(int i=0; i < 5; i++){
  // do stuff
}

The only approach I can think of is to use ugly goto statements:

loop:
  // do stuff
  goto loop;

But how can I exit this loop after exactly 5 runs? Or is there a different way?

Edit: The solution should not be recursive. Function calls are not yet allowed in the course.

You'll need at least an `if` with your goto to immitate a loop. — AliciaBytes, Apr 23 '15 at 07:39
yes: `//do stuff //do stuff //do stuff //do stuff //do stuff `. However, the point of it evades me. — amit, Apr 23 '15 at 07:40
Please explain the usefulness of this... I mean why do you NOT want to use loops and goto? — unrealsoul007, Apr 23 '15 at 07:40
To be honest: It is a small part of an assignment. But I doubt this is even possible. The answer of @amit of course works, but in reality I need 32 of them. I don't think this is the desired way. — 00FF00FF, Apr 23 '15 at 07:42
If this is course work then it is ridiculous. What is this supposed to teach you? Repeat the statement that you want five times. — gnasher729, Apr 23 '15 at 08:24

Srinath Mandava · Answer 1 · 2015-04-23T08:28:52.873

1

You can use a recursive function and pass an argument as a counter.
Decrease the counter each time before calling.

int func(int a,int counter)
{
  int c;


  // .. your logic
  return counter==0?a:func(a,counter-1);      

}

This line return counter==0?a:func(a,counter-1); helps you handling the condition when counter==0 without using if.

edited Apr 23 '15 at 08:28

answered Apr 23 '15 at 07:43

Srinath Mandava

3,384
2
24
37

Sorry, I forgot to add that recursive call are not allowed as this should be translated to assembler later and function call are yet not allowed in the assignment. – 00FF00FF Apr 23 '15 at 07:47
This is very intelligent, but it does not work. (At least in C) `error: expected expression before ‘goto’` – 00FF00FF Apr 23 '15 at 08:00
Yeah noticed that .. goto is a statement ... looking for an alternative – Srinath Mandava Apr 23 '15 at 08:03
return can only be used as a statement on its own. – gnasher729 Apr 23 '15 at 08:24

score 0 · Answer 2 · answered Apr 23 '15 at 07:51

0

You could use a foreach loop:

// An array of ints with 5 values
int[] someNumbers = new int[] {0, 1, 2, 3, 4};

// Then foreach through someNumbers
foreach (int aNumber in someNumbers)
{
    // Do Stuff
}

It is a bit of a hack but it will work fine, also if you want make someNumbers public and put it in some secluded space in your code, so it is not clogging your code up :).

answered Apr 23 '15 at 07:51

Winky2222

46
7

It would work, but foreach is also a loop statement. :( – 00FF00FF Apr 23 '15 at 07:53

score 0 · Answer 3 · answered Apr 23 '15 at 08:05

0

I found out this is not possible. Thanks for the answers anyway!

answered Apr 23 '15 at 08:05

00FF00FF

31
3

score 0 · Answer 4 · edited May 23 '17 at 12:22

If you are using GCC, you can use the feature "label as value" (you can also do similar stuff in other compilers), like this:

#include <stdio.h>

int main() {
    int n, v, c;

    static void* labels[] = {&&nope, &&again};

    n = 5;
    again:
        printf("stuff\n");
        n--;
        goto *labels[__builtin_popcount(n&-n)];        
    nope:
        printf("done!\n");
    return 0;
}

This code finds the lowest set bit in n (to reduce it to only one bit, if any) and do a popcount on it. In practice this will return 0 if the n==0 or 1 otherwise. If you don't want to rely on __buitin_popcount, you can implement your own, like this:

int popcount(int v) {
    int c;
    c = (v & 0x55555555) + ((v >> 1) & 0x55555555);
    c = (c & 0x33333333) + ((c >> 2) & 0x33333333);
    c = (c & 0x0F0F0F0F) + ((c >> 4) & 0x0F0F0F0F);
    c = (c & 0x00FF00FF) + ((c >> 8) & 0x00FF00FF);
    c = (c & 0x0000FFFF) + ((c >> 16)& 0x0000FFFF);
    return c;
}

Execute a loop x times without loop or if statements

4 Answers4