C++ for Scientists - Technische Universität Dresden

34 CHAPTER 2. C++ BASICS
} else if (weight 100.0)
if (weight > 200.0)
cout ≪ ”This is extremely heavy.\n”;
else
cout ≪ ”This is quite heavy.\n”;
It looks like the last line is executed when weight is between 100 and 200 assuming the first if
has no else-branch. But we could also assume the second if comes without else-branch and the
last line is executed when weight is less or equal 100. Fortunately, the C ++ standard specifies
that an else-branch always belongs to the innermost possible if. So, we can count on our first
interpretation. In case that the else-branch should belong to the first if we need braces:
if (weight > 100.0) {
if (weight > 200.0)
cout ≪ ”This is extremely heavy.\n”;
} else
cout ≪ ”This is not so heavy.\n”;
Maybe these examples convinced you that it is more productive to set more braces and save
the time guessing what the branches belong to.
Advise
If you use an editor that understands C ++ (like the IDE from Visual Studio
or emacs in C ++ mode) then automatic indentation is a great help with
structured programming. Whenever a line is not indented as you expected,
something is most likely not nested as you intended.
2.5.2 Conditional Expression
Although this section describes statements, we like to talk about the conditional expression
here because of its proximity to the if-statement. The semantic of
condition ? result for true : result for false
is that if the condition in first sub-expression evaluates to true then the entire expression is the
second expression otherwise the third one. For instance, we can compute the minimum of two
values with either if-then-else or the conditional expression: