Most elegant looping construct?

Question

Sorry for the newb question. I'm still learning programming. So I'm using C++, and I need to do something like this:

int n;
do {
    n = get_data();
    if(n != -1)
        send(n);
} while(n != -1);

This is just a sketch. Anyway it doesn't feel real elegant. I have to have my test twice. I could just test once and set a flag, but that doesn't feel real elegant either since I have to check the flag twice. It just seems like there should be a way to do this more easily, since it's so easy what I want to do.

Answer 1

Howabout using break:

int n;
while(1) {
    n = get_data();
    if(n == -1)
        break;
    send(n);
}

This way you only test once, and quit immediately if get_data doesn't return what you want.

Answer 2

int n;
while (-1 != (n = get_data())) {
    send(n);
} // while

Answer 3

Your original version is fine.

In my last C programming job we had to follow the MISRA coding standards.

Under the MISRA rules, this:

int n;
while(1) {
    n = get_data();
    if(n == -1)
        break;
    send(n);
}

is prohibited because of the break, and this:

while((n = get_data()) != -1) { send(n); }

is prohibited because an assignment appears in a boolean context, so I am in the habit of writing loops similar to your original version.

You could a boolean variable if you think it will make your intention clearer or if the test is a complex expression:

int n;
bool valid;
do {
    n = get_data();
    valid = n != -1;
    if(valid)
        send(n);
} while(valid);

But for a simple test like "n != -1" it may not be worth making the program longer.

Answer 4

Similar to eed3si9n's but arguably easier to read:

 int n;
 while (n = get_data(), n != -1)
 {
     send(n);
 }

Answer 5

for (int n = get_data(); n != -1; n = get_data()) {
  send(n);
}

Answer 6

Construct with a goto :)

int n;
goto inside; do {
  send(n);
inside:
  n=get_data();
} while(n!=-1);

Answer 7

int get_data()
{
 ...
}

void _send(int )
{
 ...
}

int  send(int (*a) ())
{
   int n = a();

   if (n == -1)
      return n;

   _send(n);
   return 1;
}

int main()
{
  int (*fp)();
  fp = get_data;
  while ( send(fp)!= -1 );

  return 0;
}

HTH

Answer 8

int n;
n = get_data();
while (n != -1) {
  send(n);
  n = get_data();
}

Answer 9

In Python you would do this:

while True:
    n = get_data()
    if n == -1:
        break
    send(n)

As you can see, this is not much shorter than your C version. Usually, a Python code is 5 to 10 times smaller than its C equivalent. This is not the case here, so you can enjoy your readable, short enough, fast snippet, and focus on something else.

If you do want to make it shorter, check Jonathan's answer, but really this doesn't matter.