Going through the book, currently on Chapter 4. On page 78, an example of a do while loop uses ++ as a suffix (i++) to increment, while on page 79, another example uses ++ as a prefix (++totalYears). Is there any rhyme or reason for this? It would appear that it doesn't matter as there's no other operation in the expression.

On page 67 there is a chart explaining the order of priority of the arithmetic operators. ++ used as a prefix is the highest priority. ++ used as a suffix is the lowest priority.

Carl Olsen
www.carl-olsen.com

I'm aware of the priorities, it's just that in these two examples, there's nothing else to prioritize, so I was wondering if there were some convention on which to use.

It says "i++" increments "i" after it's value has been output to the screen. If it were "++i" then it would be incremented before it was output to the screen. Run the example both ways and see what happens.


Carl Olsen
www.carl-olsen.com

The only reason is to show readers we can use two methods to do the same thing.There are differeces between them,but in the two places,they are the same.Which one will be used depends your convention.

They are not the same. Run the example both ways and you'll see that "i++" results in a list of numbers 1-10, and "++i" results in a list of numbers 2-11.

Carl Olsen
www.carl-olsen.com

It all comes down to convention, usually. People use what they know and are familiar with.

Typically, if you're writing an expression where the location of the increment operator makes a difference in the result, then I suspect that line of code is more likely to cause confusion and/or problems down the road. These lines should probably be split.

When many students first begin learning C or C++, they often feel that empty for loops are an "elegant" and/or "witty" solution to certain problems. In the real world, however, such cleverness is usually looked down upon in favor of readability.

For example:

for (int i = 0; i < 10; std::cout << i++);

should really be:

for (int i = 0; i < 10; ++i)
{
   std::cout << i;
}

The second version, while it does take a lot more room, is much easier to understand at first glance. While it's possible to perform computation in the third section of a for expression, this place is really supposed to hold some sort of operation that will bring your iteration control variable closer to the stop condition.

Also, you'll notice that in the second code snippet, I use ++i as the incrementation variable. This is because it's *slightly* more efficient (unless you have a smart compiler). Because i++ is a post-increment operator, the compiler allocates space on the stack to hold the original value of i for use in the expression, and increments i in the original location.

Since there is no "rest of the expression", this extra allocation is not used for anything and therefore is just wasted space.

Again, many compilers can determine whether a post-incrementation operation is the entire expression and suppress the extra allocation in this case. But it's still handy to be explicit.



Take care,

Nik
http://www.bigaction.org/