How Not to Program in C++

254 Part III

Answer 87: The prefix version of

++

returns the number after incrementing.

Thus

++++i;

tells C++ increment

i

, returns the result, then increments the variable

i

again.

The postfix version of

++

(i++)

returns a copy of the variable, then incre-

ments it.

So

++++i

1. Tells C++ to make a copy of

i

(call it

tmp_1

)

2. Increments

i

3. Does the rest of the work on

tmp_1

4. Makes a copy of

tmp_1

(call it

tmp_2

)

5. Increments

tmp_2

6. Returns

tmp_1

as the value of the expression

NOTE C++ won’t let you get away with

++++

on integers. Only with some added class silliness can

you get away with it.

Avoidance 31: Use

++

and

--

singly.

Answer 88: The problem is the macro:

#define SQR(x) ((x) * (x))

when called with

SQR(++number)

This expands to

((++number) * ...