C++ for Scientists - Technische Universität Dresden

2.5. CONTROL STATEMENTS 33
The expression in the parentheses must be logic expression or something convertible to bool.
For instance, one can write:
int i;
// ...
if (i) // bad style
do something();
In the example, do something is called if i is different from 0. Experienced C and C ++ programmers
know that (from heart) but the intentions of the developer are better communicated if
this is stated explicitly:
int i;
// ...
if (i != 0) // much better
do something();
The branches of if consist each of one single statement. To perform multiple operations one can
use braces: 12
int nr then= 0, nr else= 0;
// ...
if (...) {
nr then++;
cout ≪ ”In then−branche\n”;
} else {
nr else++;
cout ≪ ”In else−branche\n”;
}
In the beginning, it is helpful to always write the braces. With more experience, most developers
only write the braces where necessary. At any rate it is highly advisable to intend the branches
for better readable with any degree of experience.
An if statement can contain other if-statements:
if (weight > 100.0) {
if (weight > 200.0)
cout ≪ ”This is extremely heavy.\n”;
else
cout ≪ ”This is quite heavy.\n”;
} else {
if (weight < 50.0)
cout ≪ ”A child can carry this.\n”;
else
cout ≪ ”I can carry this.\n”;
}
In the above example, the parentheses could be omitted without changing the behavior but it
is clearer to have them. The example is more readable if we reorganize the nesting:
if (weight < 50.0) {
cout ≪ ”A child can carry this.\n”;
} else if (weight