Go with a ";" at the beginning of the loop, which means

Question

I picked up a code with a code like this:

for (; indField > 0 && indMask > 0; )

What does that mean ";" at the beginning and end of the command?

Answer 1

The for has 3 "parts":

for ( executar antes de começar ; condição para executar ; executar ao fim da iteração )

You only need to fill in what you need. But you have to put the ; anyway.

In this case, the author of the code did not need to do anything to initialize the loop, only interested him the condition to iterate, which is the middle item.

Likewise, if he wanted a loop infinite, it would be enough to also omit the condition:

for( ;; ) {
   // ficarei em loop até o fim dos tempos (ou alguma coisa externa me parar)
}

Answer 2

The person should have used one while in this case, after all has only one condition and nothing else. The wisest would be:

while (indField > 0 && indMask > 0)

In that case the structure should not be a for Because you don’t use what he has to your advantage. The confusion of the AP that originated the question was precisely because the programmer did not follow the basic precept of doing what is most semantically correct, which is what he and everyone should do. At the very least is more elegant use the while there.

Technically, it means you didn’t want to initialize a variable, as is common to do in a for. also did not want to execute anything at every step of loop iteration, noted that there is nothing also after the last ;?.

A for is:

for (           //o comando
    int i = 0;  //a inicialização da variável (geralmente, pode ser qualquer ação)
    i < 10;     //a condição de término do laço (sempre tem que ser um resultado booleano
    i++         //o passo a executar em cada interação, o incremento é muito comum
) {             //fecha o comando e abre o bloco de execução

Note that the for is always composed of 3 stocks different and then usually have a block of what should be executed in the loop. In theory all 3 parts can be omitted depending on what you want.

Other things that few people know is that there can be more than one expression in each of these parts, separating by commas, and that’s not unique to for, is valid in any context where a statement. Example:

for (int i = 0, j = 0; i < 10; i++, j++) { ... }

I put in the Github for future reference.

Even the condition can do this, but only the last boolean expression will be considered as the final result to determine whether the loop should continue or not.

So each of the 3 statements of for can have from zero to "infinite" expressions.

Behold What’s the difference between while, for, while and foreach?. It’s another language, but it’s worth the same.