C++ for Scientists - Technische Universität Dresden

2.5. CONTROL STATEMENTS 37
Here it was simpler to take out term 0 and start with term 1. We also used less-equal to assure
that the term x 10 /10! is considered.
The for-loop in C ++ is very flexible. The initialization part can be any expression, a variable
declaration or empty. It is possible to introduce multiple new variables of the same type. This
can be used to avoid repeating the same operation in the condition, e.g.:
for (int i= xyz.begin(), end= xyz.end(); i < end; i++) ...
Variables declared in the initialization are only visible within the loop and hide variables of the
same names from outside the loop.
The condition can be any expression that can be converted to a bool. An empty condition is
always true and the loop is repeated infinitely unless from inside the body as we will discuss
in the next section. We said that loop indices are typically incremented in the head’s third
part. In principle, one can modify it within the loop body but programs are much clearer if it
is done in the loop head. On the other hand, there is no limitation that only one variable is
increased by 1. One can modify as many variables as wanted using the comma operator and by
any modification desired such as:
for (int i= 0, j= 0, p= 1; ...; i++, j+= 4, p∗= 2) ...
This is of course more complex than having just one loop index but still more readable than
declaring/modifying indices before the loop or inside the loop body.
In fact, the for-loop in C and C ++ is just another notation of a while-loop. Any for-loop:
for (init; cond; incr) {
st1; st2; ... stn;
}
can be written with a while-loop:
{
}
init;
while (cond) {
st1; st2; ... stn;
incr;
}
Conversely, any while-loop can evidently be written as for-loop. We do not know if there is
a design guideline from a software engineering guru when to use while or for but for is more
concise if there is a local initialization or some incremental operation.
2.5.5 Loop Control
There are two statements to deviate from the regular loop evaluation:
• break and
• continue.
A break terminates the loop entirely and continue ends only the current iteration and continues
the loop with the next iteration, for instance: