Loops based on a flowchart

Question

How do I write the code for a loop based on this flowchart? It has a do...while. Peeciso of a simple and direct response with nested loops.

Answer 1

That flow, tell me this:

1. Perform task A
2. Compare B; If it comes true, get out of the loop
3. Perform the task C
4. Go back to step 1

Note that the flow in step 4 is an unconditional deviation returning to step 1. This deviation ends up creating an infinite loop (while B not satisfied). In general, I would do so:

while (true) {
  // passo 1
  // passo 2
  // passo 3
}

Step 4 is represented by the flow control provided by while. Filling in a few more gaps, we get:

while (true) {
  A();
  // passo 2
  C();
}

Assuming A() and C() are the methods called in steps 1 and 3. It may be anything, but I represented by methods.

On step 2, it involves a conditional on B. There is no case senão. So, by and large:

while (true) {
  A();
  if (B()) {
    // ação caso B seja verdadeiro
  }
  C();
}

The action to get out of the loop is with the break. So:

while (true) {
  A();
  if (B()) {
    break;
  }
  C();
}

---

Using the language dot to describe your diagram, I obtained the following:

I am only republican-here because I will use this language to do some manipulations in the structure of the tie and generate other equivalents, so the idea is to lessen the strangeness.

The loop structure is equivalent to the expression:

AB(CAB)*

Why do I say this? Simple, because initially A and B are executed and, depending on that result, executed C, afterward A (back in the loop) and then B again, to make the decision as to where to go.

The following description is the translation of the expression. Note that this step-by-step is equivalent to the first.

1. Perform task A
2. Until B, do:
   1. Execute C
   2. Execute A

Compared to the previous scheme, I no longer needed a step of unconditional deviation, I used a "while". I copied the command that was pre-conditional to the end of the loop, so that it runs at the right time the same amount of times.

The flowchart is now drawn like this:

In code, the while becomes a while. The rest stays the same:

A();
while (!B()) { // perceba que eu só repito enquanto `B()` for falso, já que `B()` é a condição de saída
  C();
  A();
}

---

Still using flowchart 2, we can do using the for. I don’t like this alternative, but it works.

A();
for (; !B(); A()) {
  C();
}

---

Changing the for, we get the following:

A();
for (; !B(); C(), A());

---

We can do the for as infinite loop also:

for (;;C()) {
  A();
  if (B()) {
    break;
  }
}

---

If you insist on doing the verification after the operations, this operation must necessarily be after all the operations. For this, we can define that the rodable initial be only A, assign to the rodable the execution of C and then A and then make the conditional check:

Runnable rodavel = () -> { A(); };
do {
  rodavel.run();
  rodavel = () -> { C(); A(); };
} while (!B());

---

We can also control differently the way the operation is run C. We can control through a flag mnemonically named deveExecutarC, which starts as false but, at the end of the loop, is assigned the true value in it:

boolean deveExecutarC = false;
do {
  if (deveExecutarC) {
    C();
  }
  A();
  deveExecutarC = true;
} while (!B());

---

We can try to assign the flag value several times by placing this assignment within the block else:

boolean deveExecutarC = false;
do {
  if (deveExecutarC) {
    C();
  } else {
    deveExecutarC = true;
  }
  A();
} while (!B());

---

This problem could be solved recursively as well:

private void executaRecursivo() {
  C();
  A();
  if (!B()) {
    executaRecursivo();
  }
}

private void fluxograma() {
  A();
  if (!B()) {
    executaResursivo();
  }
}

Just call the method fluxograma and you will get the same execution.

---

We can set the recursion differently, passing a parameter to it. The idea is the same as the do-while with the flag deveExecutarC:

private void fluxograma(boolean deveExecutarC) {
  if (deveExecutarC) {
    C();
  }
  A();
  if (!B()) {
    fluxograma(true);
  }
}

private void fluxograma() {
  fluxograma(false);
}

To get the desired result, just call fluxograma(), unencumbered.

---

More variation with recursion:

private void recursao() {
  if (!B()) {
    C();
    A();
    recursao();
  }
}

private void fluxograma() {
  A();
  recursao();
}

As usual, just call fluxograma().

---

A friendlier variation of the previous recursion:

private void recursao() {
  if (B()) {
    return;
  }
  C();
  A();
  recursao();
}

private void fluxograma() {
  A();
  recursao();
}

As usual, just call fluxograma().

---

Another variation:

private void fluxograma() {
  A();
  if (B()) {
    return;
  }
  C();
  fluxograma();
}

As usual, just call fluxograma().

---

One more recursion, inspired in this answer, unfolding Indirect function recursion, function pointer:

private void fluxograma() {
  A();
  Runnable funcaoSaida = B()? () -> {}: () -> { C(); fluxograma(); };
  funcaoSaida.run();
}

As usual, just call fluxograma().

---

If you do not want the variable:

private void fluxograma() {
  A();
  (B()? (Runnable) () -> {}: (Runnable) () -> { C(); fluxograma(); }).run();
}

As usual, just call fluxograma().