1
CS 112 Introduction to
Programming
Lecture #14:
Variable Scope and Duration;
Program Development Process
and Stepwise Refinement
http://flint.cs.yale.edu/cs112/
2
Outline
rAdmin. and review
qMore about defining and using methods
¦Method header
¦Overloading and signature
¦Method parameter passing
¦Method body
¦Variable scope and duration
rProgram development process
rStepwise refinement using the Calendar
program as an example
3
Review: Method Overloading
rMethod overloading is the process of using
the same method name for multiple methods
mUsually perform the same task on different data types
rThe compiler determines which version of the
method is being invoked by analyzing the
parameters, which form the signature of a
method
mIf multiple methods match a method call, the compiler picks
the best match
mIf none matches exactly but some implicit conversion can be
done to match a method, then the method is invoked with
implicit conversion.
4
More Examples
double TryMe ( int x )
{
return x + 5;
}
double TryMe ( double x )
{
return x * .375;
}
double TryMe (double x, int y)
{
return x + y;
}
TryMe( 1 );
TryMe( 1.0 );
TryMe( 1.0, 2);
TryMe( 1, 2);
TryMe( 1.0, 2.0);
5
Recap: Parameter Passing
rTwo types of parameter passing:
mCall by value: a modification on the formal argument has no
effect on the actual argument
mCall by reference: a modification on the formal argument can
change the actual argument
mDepend on the type of a formal argument
rFor C# simple data types, it is call-by-value
rChange to call-by-reference: ref or out
mThe ref or out keyword is required in both method
declaration and method call
mref requires that the parameter be initialized before enter a
method
mout requires that the parameter be set before return from a
method
Outline
RefOutTest.cs
1// RefOutTest.cs
2// Demonstrating ref and out parameters.
3
4using System;
5using System.Windows.Forms;
6
7class RefOutTest
8 {
9// x is passed as a ref int (original value will change)
10 static void SquareRef( ref int x )
11 {
12 x = x * x;
13 }
14
15 // original value can be changed and initialized
16 static void SquareOut( out int x )
17 {
18 x = 6;
19 x = x * x;
20 }
21
22 // x is passed by value (original value not changed)
23 static void Square( int x )
24 {
25 x = x * x;
26 }
27
28 static void Main( string[] args )
29 {
30 // create a new integer value, set it to 5
31 int y = 5;
32 int z; // declare z, but do not initialize it
33
When passing a value by reference
the value will be altered in the rest
of the program as well
Since x is passed as out the variable
can then be initialed in the method
Since not specified, this value is defaulted to being
passed by value. The value of x will not be changed
elsewhere in the program because a duplicate of the
variable is created.
Since the methods are void
they do not need a return value.
