Visual Basic.NET How to Program (PDF)

Chapter 6 Procedures 195
Method Description Example
Sqrt(x) returns the square root of x Sqrt(9.0) is 3.0
Sqrt(2.0) is 1.4142135623731
Tan(x) returns the trigonometric
tangent of x (x in radians)
Tan(0.0) is 0.0
Fig. Fig. 6.7 6.7 Math class methods (part 2 of 2).
Software Engineering Observation 6.9
It is not necessary to add an assembly reference to use the Math class methods in a program,
because class Math is located in namespace System, which is implicitly added to all console
applications. 6.9
6.6 Argument Promotion
An important feature of procedure definitions is the coercion of arguments (i.e., the forcing
of arguments to the appropriate data type so that they can be passed to a procedure). Visual
Basic supports both widening and narrowing conversions. Widening conversion occurs
when a type is converted to another type (usually one that can hold more data) without losing
data, whereas a narrowing conversion occurs when there is potential for data loss during
the conversion (usually to a type that holds a smaller amount of data). Figure 6.8 lists
the widening conversions supported by Visual Basic.
For example, the Math class method Sqrt can be called with an Integer argument,
even though the method is defined in the Math class to receive a Double argument. The
statement
Console.Write(Math.Sqrt(4))
correctly evaluates Math.Sqrt(4) and prints the value 2. Visual Basic promotes (i.e.,
converts) the Integer value 4 to the Double value 4.0 before the value is passed to
Math.Sqrt. In this case, the argument value does not correspond precisely to the parameter
type in the method definition, so an implicit widening conversion changes the value to
the proper type before the method is called. Visual Basic also performs narrowing conversions
on arguments passed to procedures. For example, if String variable number contains
the value "4", the method call Math.Sqrt(number) correctly evaluates to 2.
However, some implicit narrowing conversions can fail, resulting in runtime errors and
logic errors. For example, if number contains the value "hello", passing it as an argument
to method Math.Sqrt causes a runtime error. In the next section, we discuss some
measures the programmer can take to help avoid such issues.
Common Programming Error 6.7
When performing a narrowing conversion (e.g., Double to Integer), conversion of a
primitive-data-type value to another primitive data type might change the value. Also, the
conversion of any integral value to a floating-point value and back to an integral value could
introduce rounding errors into the result. 6.7