Understanding Methods, Menus, and Dialog Boxes in Programming, Slides of C programming

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Methods, Menus, and Dialog Boxes

05_methods_menus.ppt

Overview of Topics

• Top-Down Design
• Built-in Methods
• Black Box Analogy
• Programmer-Defined Methods
• Method’s Signature & Overloading
• Pass-by-value Arguments
• Menu Designer
• Context Menus (right-click)
• Common Dialog Boxes

Top-Down Design - Analogy

• A design method where the major task to

be accomplished is divided into subtasks.

• Major Task: clean house
• Subtasks: dust, vacuum, sweep, mop
• Programming example.
• Major Task: CS5 Sales Calculator
• Subtasks: input qty, price calculate sales tax, shipping, subtotal, etc display total bill

Subtasks

• Each subtask should perform a single well-defined task.
• Each subtask may produce some result.
• Treat them as small programs.

Input -> Process -> Output

• These subtasks can be used at different times in

one program or placed in a library and used by many different programs.

• The int.Parse method is a complicated task that

converts strings to numbers, and is used by many different programs.

Programmer-Defined Methods

• Before coding some programmer-defined

methods, let’s look at some built-in methods

a little closer.

• It will help understand what we are trying to

develop if we look at how methods are used.

Built-in Methods

• They are like small programs.
• They have their own input – process – output.
• They can have one or more inputs.
• But methods can only return one output.
• As programmers, we don’t get to see the code

(process) of built-in methods.

• The process is like a black box…

Convert Text to Integer – int.Parse

• Convert Text to Integer method is named int.Parse.
• The documentation for int.Parse states the value that will be returned, method name, and the type and number of arguments. intNumber = int.Parse(String) returnedValue = MethodName (arguments)
• Int.Parse takes one argument that is a String.
• The method is called using the following syntax:

If txtQuantity.Text contains “3” then the function call:

intNumber = int.Parse(txtQuantity.Text)

would return a value of 3 into intNumber.

Method Call

• We issue a method call when we use it.
• Processing control is passed to the method

until it completes its task and returns control

back to the calling method.

• Most methods return a value back,

but only one value can be returned

through the return statement.

Method’s Signature & Overloading

• Method overloading occurs when more than one method with the same name is defined, but differ in the parameter list.

MessageBox.Show(TextMessage); MessageBox.Show(TextMessage, TitleBar); MessageBox.Show(TextMessage, TitleBar, ButtonType); MessageBox.Show(TextMessage, TitleBar, ButtonsType, Icon);

• Each method’s signature is unique and consists of:
  • Method name
  • The number, data types, and order of its parameters
  • Parameters can also be modified with the keywords ref and out (These keywords are covered in next powerpoint presentation)
  • The signature does NOT include the data type of the returned value and the names used to identify the parameters.

Small Programs

• Think of each method as a small program with

input, process, and output steps.

Output < Process < Input

returnedValue = MethodName (arguments)

intNumber = int.Parse(String)

Function Definition - Syntax

• Syntax: private dataType MethodName(arguments) { statement(s) return expression; }
• dataType is where we specify what type of value is being returned, string or numeric.
• Use the return statement to return the value.
• Variables that will be used to store the values sent into the method are listed in parentheses as arguments.

Method Definition - Example

private decimal calcExtendedPrice(int intQty, decimal decPrice) { decimal decExtendedPrice; decExtendedPrice = intQty * decPrice; return decExtendedPrice; }

• decimal is the data type of the value being returned.
• calcExtendedPrice is the Method Name.
• intQty and decPrice are the arguments passed to method.
• The signature of this method is calcExtendedPrice(int, decimal)

Multiple Returns

• A method may be defined with multiple Return statements.
• The first Return statement executed returns the value and returns processing control back to the calling procedure.

private decimal calcExtendedPrice(int intQty, decimal decPrice { if (intQty < 26) return intQty * decPrice; else return intQty * (decPrice * .95); //5% discount }

Single Return Preferred

• Although methods can be coded using multiple Return statements, one Return statement is preferred.
• Having multiple Returns in complex procedure can be difficult to maintain and debug.

private decimal calcExtendedPrice(int intQty, decimal decPrice ) { decimal decExtendedPrice; if (intQty < 26) decExtendedPrice = intQty * decPrice; else decExtendedPrice = intQty * (decPrice * .95); // 5% discount

return decExtendedPrice; }