imitations

Hi!

I'm new to the boards, yet not new to forum posting and programming (have been doing both for almost half a decade), I hope I can have a nice stay here and see how it goes

I'm currently learning C++ and would like to know something; I know that many of the loops in C/C++ can be represented using a regular while loop. In the following examples, please correct me if I'm wrong:

Representing a while-statement using a do-statement

Code:

do
{
     if (/* condition */) 
     {
          // ...
     }
     else
          break;
} while (true);

Representing a for-statement using a do-statement

Code:

int i = 0;
do
{
     if (i < MAX)
     {
          // ...
          i++;
     }
     else
          break;
} while (true);

Representing a while-statement using a for-statement

Code:

for (; /* condition */;)
{
     // ...
}

Representing a do-statement using a for-statement

Code:

// the statements go here...
for (; /* condition */;)
{
     // same statements as above...
}

These are my guesses at the moment. Please feel free to correct me if I happened to make a mistake in any of those or if you see that any of them are inefficient (say, if I included something that was not necessary and there is a better way to represent the same thing, etc.)

Thanks!

Your last one is somewhat incorrect, since do-while ALWAYS executes at least once, so the correct solution would be:

Code:

for(;;)
{
   ...
   if(condition)
      break;
}

Of course, if condition is not true before the loop, you won't notice the difference.

I tend to use "do - while" specifically when I want something done AT LEAST once - e.g. reading and validating data from user - you want to read in the value once at least, then if that's not an OK value, you repeat, until you get a valid value.

I use while when I have an unknown number of iterations, and sometimes the loop is not needed at all.

For-loops I choose when there is something that we can somehow "count" across. This is not strictly just incrementing a variable or some such - I'm happy using for-loops to iterate across a linked list for example.

--
Mats

Yeah a classic case of use for a do ... while comes from manually implementing a function for converting a number to string. You always want at least one digit.

The first one could be simplified to:

Code:

do
{
     if ( ! /* condition */) 
          break;
     // ...
} while (true);

But you could also do it like this:

Code:

if (/* condition */) 
     do
     {
          // ...
     } while (condition);

The assembly that actually gets generated goes as far as doing it like this:

Code:

goto loopend;
do
{
     // ...
     loopend:
} while (condition);

The second one:

Code:

// initialisation part
do
{
     if (! /* condition */ )
          break;
     // ...
     // next iteration part
} while (true);

For loops don't have to count over values. They can for example, walk over a linked list.

Originally Posted by iMalc

The assembly that actually gets generated goes as far as doing it like this:

Code:

goto loopend;
do
{
     // ...
     loopend:
} while (condition);

Yes, we can probably trust MOST compilers to do that - but not all.

--
Mats