Teach Yourself Borland C++ in 14 Days - portal

Up to Your Neck in C++
Now the compiler knows to treat the literal values as ints. A cast is also used to temporarily
force the compiler to treat one data type as if it were something else. Let’s go back to the first
example in this section and this time cast one of the variables to remove the ambiguity:
int x = 5;
float y = 10.5;
float result = multiply((float)x, y);
In this case x is an int, but you are casting it to a float, thereby telling the compiler to treat
it as a float. The compiler happily calls the float version of multiply() and goes on its way.
Ultimately, you want to write overloaded functions so that ambiguities do not exist and
casting is not necessary. In some cases that is not possible, and in those cases casting will be
required.
Default Parameters for Functions
NEW TERM
A function in C++ can have default parameters which, as the name implies, supply
a default value for a function if no value is specified when the function is called.
A function implementing a default parameter might look like this:
// declaration, parameter ‘eraseFirst’ will be false by default
void Redraw(bool eraseFirst = false);
// definition
void Redraw(bool eraseFirst)
{
if (eraseFirst) {
// erase code
}
// drawing code
}
When this function is called, it can be called with or without a parameter. If the parameter
is supplied at the time the function is called, the function behaves as a regular function would.
If the parameter is not supplied when the function is called, the default parameter is used
automatically. Given this example, the following two lines of code are identical:
Redraw();
Redraw(false);
Note that when a parameter has a default value, it can be omitted from the function call
altogether. You can mix default and non-default parameters in the same function:
int PlaySound(char* name, bool loop = false, int loops = 10);
// call function
int res;
res = PlaySound(“chime.wav”); // does not loop sound
res = PlaySound(“ding.wav”, true); // plays sound 10 times
res = PlaySound(“bell.wave”, true, 5); // plays sound 5 times
89
3