Sams Teach Yourself C++ in 24 Hours, Third Edition

Default Parameters

For every parameter you declare in a function prototype and definition, the calling function must pass in a value. The value passed in must be of the declared type. Thus, if you have a function declared as

long myFunction(int);

the function must, in fact, take an integer variable. If the function definition differs, or if you fail to pass in an integer, you will get a compiler error.

The one exception to this rule is if the function prototype declares a default value for the parameter. A default value is a value to use if none is supplied. The preceding declaration could be rewritten as

long myFunction (int x = 50);

This prototype says “myFunction() returns a long and takes an integer parameter. If an argument is not supplied, ...