Mixing types

You need to be careful when mixing different data types. C++ will implicitly cast objects to the more general type, sometimes with unexpected consequences. Later we’ll see how to explicitly cast data if needed.

Try it…

Try the following (you’ll need to put this in a main() function and compile it):

// convert from Fahrenheit to Celsius

double T_F {100.0};
double T_C =  (T_F - 32) * (5 / 9);

std::cout << "T_C = " << T_C << std::endl;

Why doesn’t this work as expected?

Casting

We can use static_cast to explicitly convert one type to another. For example:

int a{5};
double x = static_cast<double>(a);

will convert the integer a to a double-precision floating point object x.

Note

There is a new pattern here, the use of <>—this is used in template functions, a topic we will talk more about later.

In this case, by putting <double> we are telling the compiler to use a version of static_cast that operates on a double object.

There are other types of casts in C++, but this is the one we will use the most.

Try it…

Let’s explicitly cast the integers in the program above to see if it fixes our problem.