Question

I was wondering if anyone could suggest to me how to implement this loop in the following pseudocode:

8: loop
9: while f[0] = 0 do
10: for i = 1 to N do
11: f[i ¡ 1] = f[i]
12: c[N + 1 – i] = c[N – i]
13: end for
14: f[N] = 0
15: c[0] = 0
16: k = k + 1
17: end while
18: if deg(f) = 0 then
19: goto Step 32
20: end if
……… …… ….
31: end loop

My question is how I should implement the loop that starts on line 8 and ends on 31; I am comfortable with the statements between lines 8 to 31, but what kind of loop do I use on line 8, and what conditions do I give for the loop?

Thanks in advance.

Answer 1

That’s an infinite loop. No conditions, just loop forever. The only way out is to get to step 19. In C-like languages you can write that as while (true) or for (;;):

for (;;) {
    // ...

    if (deg(f) == 0) {
        goto afterLoop;
    }

    // ...
}

afterLoop:
// ...

goto is frowned upon, though. It’d be better to replace goto Step 32 with a break statement, which exits a loop immediately:

for (;;) {
    // ...

    if (deg(f) == 0) {
        break;
    }

    // ...
}

For what it’s worth, if you didn’t have steps 21-30 you could use a do/while loop, where the loop condition goes at the bottom of the loop instead of the top:

do {
    // ...
}
while (deg(f) != 0);

That would work if lines 18-20 were the final lines in the loop. Since they’re not, it looks like option #2 is the one to go with.