Before we even start to consider what a program is we need to understand how data is stored and manipulated in a computer: 

	Data is stored in various parts of the computer hardware
	These hardware parts have physical limits imposed on them by various design constraints this imposes a limit on the size of a word or number one can represent and store within these hardware parts
	The size of the data (word or number or picture) is measured in Bits or Bytes  (1 Byte = 8 Bits) 1 Byte is the amount of data required to represent 1 character in a computer We also have more types of unit definitions:

Name	Exact Measure	Approximate Measure
KiloByte or KB	= 1024 Bytes	1000 Bytes
MegaByte or MB	= 1024*1024 Bytes	1,000,000 Bytes
GigaByte or GB	= 1024*1024*1024 Bytes	1,000,000,000 Bytes
TeraByte or TB	= 10244 Bytes	1,000,000,000,000 Bytes

	A bit represents one of two binary states we usually represent these as 0 or 1  it is the smallest unit of storage capacity used in reality a bit may be a positive or negative voltage, a electrostatic charge, a magnetised element,...
	Bit size to represent data has increased as technology has improved.  Today 32 and 64 bit computing is common in PCs, super computers use 1024 bits and more to represent individual pieces of data The more bits you can move around per CPU operation the faster your PC can perform calculations

 The use of Bits raises the question of  what decimal number does the binary number stored in a computer 1110011011110110 represent in our number system (decimal)?

Clearly we need to be able to covert a number defined in a particular number base to decimal number base and visa-versa. Typical number bases used in computing are as follows:

	binary - number base 2
	octal - number base 8
	hex - number base 16

A table of numbers and their representation in different number bases:

Examples of number conversion:

	Convert a number AB12n in a base n to decimal = A*n3 + B*n2 +1*n1 +2*n0
	Convert 123410 to an equivalent  number in base 16 1234 / 16 =  77 rem 2 77 / 16 = 4 rem 13 4 / 16 = 0 rem 4

Therefore 1234₁₀ = 4D2₁₆

PROGRAMMING:

	We assume here that we are using sequential processing rather than parallel processing to solve our problems.
	An application (program) is a set of ordered instructions to the CPU telling it what to do and is a solution to a particular problem or set of problems
	Programs that are "running" are usually stored in RAM
	When an instruction is sent to the control unit (see CPU diagram) it is “Fetched”, Decoded to CPU language and Executed this is called the F-D-E cycle
	Instructions are executed one at a time and in some specific sequence

        TYPICAL STRUCTURE OF A CPU

	More than one program can be stored in RAM and the CPU has to switch between the instructions of each program doing the F-D-E cycle. This switching process is called “Multitasking”.
	However because the CPU is so fast it seems to us that instructions (programs) are executed in parallel BUT this is NOT parallel processing.
	Parallel processing is when there is more than one CPU performing different tasks of the same program(s) at the same time.

Instructions (code) can be written in different languages

	Machine Code most basic code combination of 1 & 0 s but difficult for humans to understand
	Assembler Code, different types depends on brand of CPU (i.e. Motorola, Intel) easier than machine code but still far from the usual way people express problems
	High Level Languages Visual Basic, C, C++, Pascal, Java,… easier than the previous types closer to how people express problems

Programs are not just written the following steps need to take place, This process is called the Program Development Life Cycle (PDLC)

	Analysis of the “problem”
	Design of the program using some method (methodology Top Down, Bottom Up, OOD,…)
	Coding of the program
	Testing of the program
	Documentation
	Maintenance of Program

Structured programming or structured design

	Is a methodology to help translate a problem into a program
	We can use flowcharts,  to help us get the solution in a graphical way
	We can use pseudo-code, a  set of instructions written in your own spoken language

Example of a Flowchart:

 

Sequence Control Structure in Visual Basic Language (VBL): This is how we write lines on code using the correct syntax (i.e. rules of grammar) and in the correct order. These lines of code tell the computer what to do. We can refer to a set of lines of code as a Block of Code or Code Block Lbl_Input1.Caption = "Please Enter an Integer Number" Lbl_Input2.Caption = "Please Enter another Integer Number" Sum = Num1 + Num2 Result = Val(Text1.Text) + Val(Text2.Text) Lbl_Output.Caption = "The sum of the two numbers is = " & Result

Selection Control Structures in VBL Selection control structures are used to make decisions in the program and control  which code statements are executed and which are not. IF - END IF  If Val(Txt_Num2.Text) = 0 Then         Print "Input is Valid Division by Zero" End If   IF - ELSE - END IF If Val(Txt_Num2.Text) = 0 Then         ' if the test condition above is true we do this        Result =  Val(Txt_Num1.Text) / Val(Txt_Num2.Text)         Print    Result Else         ' if the test condition above is false we do this         Print  "Input is NOT Valid Division by Zero" End If   IF - ELSEIF-ELSE - END IF If Val(Txt_Num2.Text) > 0 Then         ' if the test condition above is true we do this +ve answer         Result =  Val(Txt_Num1.Text) / Val(Txt_Num2.Text)         Print    Result ElseIf  Val(Txt_Num2.Text) < 0 Then         ' if the test condition above is true we do this -ve answer         Result =  Val(Txt_Num1.Text) / Val(Txt_Num2.Text)         Print    Result Else         ' if the test condition above is false we do this         Print  "Input is NOT Valid Division by Zero" End If

The Select Case is similar to the IF-ELSEIF-...-ELSE-END IF

	Select Case  test-expression
	Case expression1
	'do these code statements
	Case expression2
	'do these code statements
	Case Else
	'do these code statements
	End Select

Repetition (Loop) control structures in VBL These structures are used to execute any code statements inside the Loop many times. For  control structures are used when we know exactly the numbers of times we want to execute the code inside the loop. VBL code to add all the integer numbers between 0 and 10 inclusive: Sum = 0.0 For j = 0 to 10     Sum = Sum + j Next   VBL code to add the numbers 0, 0.5, 1.0, 1.5,...,10: Sum = 0.0 For Count = 0 to 10 Step 0.5     Sum = Sum + Count Next

Do - Until control structures are used when we DON'T KNOW exactly the numbers of times we want to execute the code inside the loop

	Do Until User_Input = "x" Or "X"
	Print  Enter a number to add to previous TO Exit type x or X
	j = Val(Txt_Num1.Text)
	Sum = Sum + j
	Loop

Nested control structures: The process of putting a code structure like the If, For & Do inside another If, For or Do is called NESTING. This nesting gives us more power in doing certain types of things. Example of Nested For and If structures: For Count1 = 0 to 10     For Count2 = 0 to 99         Sum = Sum + Count1*Count2         If Sum < 10 Then                 If Sum > 20 Then                     Label1.Caption = Sum                 Else                     Label2.Caption = Sum                 End If         Else                 Label3.Caption = Sum         End If     Next Next

Array control structures give us the power to store similar types of data together and be able to use the data quickly. Lbl_Name(0).Caption = "John" Lbl_Name(9).Caption = "Mary"

 

EXAMPLE of the design steps of a simple program PROBLEM DEFINITION:

          You are to design a program that performs the following:

 In  your design you can use either Pseudo-Code or a Flow Chart remember.  Note that the General Algorithm has the following steps:

1. Start

2. Input

3. Processing

4. Output

5.  End

A SOLUTION to the Calculate Area program USING PSEUDO CODE:

	LEVEL 1 PSEUDO CODE: 1. Start 2. Input 2.1 Display message to user to enter the radius and what units are used 3. Process 3.1 Calculate area of circle 4. Output 4.1 Display value of the area in suitable units on screen 5. End
	LEVEL 2 PSEUDO CODE: After some more thought and questions!!! 1. Start define PI as a constant 2. Input 2.1 Display message to user to enter the radius 2.2 Display units of Radius 3. Process 3.1 Calculate area of circle using Area = PI*Radius2 4. Output 4.1 Display value of circle area on screen 4.2 Display units of circle area 5. End
	LEVEL 3 PSEUDO CODE: Is after even more thought and we start to introduce code statements
	1. Start 1.1  Use form, labels, textbox, command button objects for interface
	2. Input 2.1 Display message to user to enter the radius 2.1.1 Use Label1 object to display message mentioned in 2.1 2.2 Display units of radius 2.2.1 Use Label1 object to display message mentioned in 2.2 2.2.2 Set .Caption in Properties window to -> Enter the radius in cm
	3. Process 3.1 Calculate area of circle using Area = PI*Radius2 3.1.1 Use Text1 object to get value of Radius 3.1.1.1 Use .Text property of object Text1 3.1.1.2 Set the .Text property in Properties window to blank 3.1.2 Use formula Area = PI *Val (TxtRadius .Text)^2 inside Command Button named Command1 a better name for Command1 control is e.g. CmdArea
	4. Output 4.1 Display value of circle area on screen and units of area           4.1.1 Use Label2 to display calculated area and units           4.1.2 Set .Caption in Properties Window to blank           4.1.3 Use LblArea.Caption = Area inside Command Button
	5 End