3.2. Converting from
As I mentioned, C++ converts
int s to
double s automatically if necessary,
because no information is lost in the translation. On the other hand,
going from a
double to an
int requires rounding off. C++ doesn’t perform
this operation automatically, in order to make sure that you, as the
programmer, are aware of the loss of the fractional part of the number.
The simplest way to convert a floating-point value to an integer is to use a typecast. Typecasting is so called because it allows you to take a value that belongs to one type and “cast” it into another type (in the sense of molding or reforming, not throwing).
The syntax for typecasting is like the syntax for a function call. For example:
double pi = 3.14159; int x = int (pi);
The int function returns an integer, so x gets the value 3. Converting to an integer always rounds down, even if the fraction part is 0.99999999.
For every type in C++, there is a corresponding function that typecasts its argument to the appropriate type.