Level 3 Computing Year 2 Lecturer: Phil Smith

Transcription

1 Level 3 Computing Year 2 Lecturer: Phil Smith

2 Previously We started to build a GUI program using visual studio 2010 and vb.net. We have a form designed. We have started to write the code to provided the functionality required.

3 Today We will complete the coding for our form based application. Start VS2010 and open your project. Follow my lead.

4 What have we done? We created an Event driven programming. We then developed code using procedural programming techniques. This is precisely how programs are developed in industry.

5 Console based application? Let s create the same age calculation program but this time as a console based application. Start VS2010 Create a new vb.net console application object. Code tutorial.

6 What have we done? We have now developed a console based application to calculate the age for a person based on the date entered into the program. And we have covered several key features of procedural programming:

7 Key features so far Global variables. Local variables. Procedures (sub routines). Functions. Parameters.

8 Variables Global variables. Can be seen and used by all code. declared outside of methods, functions and subroutines Local variables. Can only be seen by code in the procedure or function in which it was declared. Cannot be called or used by any other part of the program Variables have a data type: integer, string, boolean etc

9 Procedures Called from your code (not an event handler) Procedure Also called subroutine. Does not return a value. Function/method Always return a value (any data type) is a self-contained block of code: a segment of code you create yourself, and that can be used whenever you want it.

10 Parameters In Visual Basic (and other languages), you can pass an argument (variable) to a procedure by value or by reference. ByVal in the parameter list makes a copy of the data first and passes this copy to the procedure/function. ByRef in the parameter list makes a reference or link to the data, this is used for objects. This is particularly relevant to local variables. Parameters can be of any data type.

11 Parameters Example of ByVal: Private Function CalculateAreaFromRadius(ByVal radius as double) As Double Dim dblradiussquared as double Dim dblresult as Double dblradiussquared = radius * radius dblresult = dblradiussquared * Math.PI

12 More Key features We now need to look at these key features. Pre-defined functions. Modularity. Programming libraries.

13 Modularity Programmers like to break up their code into being much smaller parts: Manages complexity These are easier to write/read/understand/debug These separate blocks of code are what's called subroutines/functions/data/etc. They are stored inside of separate code modules. When we launch the program, these modules are then called. Modules are re-usable. One example of this is class libraries, these are compiled into separate dynamic link libraries (dll s).

14 Programming Libraries The Base Class Library (BCL) is a Common Language Infrastructure (CLI) standard library available to all CLI languages. CLI includes the BCL in order to encapsulate a large number of common functions, such as file reading and writing, graphic rendering, database interaction, and XML document manipulation Makes the programmer's job easier. An example is using the Math library to do specialist maths functions.

15 Programming Libraries Mainly used with classes Can be created yourself Usually added to your program The.NET Framework is a class library

16 Summary We have written two programs: A GUI based application, And a console based application. They both did the same thing. We then reviewed the key features of procedural programming.