1. Language Constructs
Construct means to build or put together. Language constructs refers to those parts which make up a high level programming language.
Features:
String Operations
Formatting input/output
Control Structure (Sequence, repetition and selection)
Data Storage (Local and Global variables, scope)
Data Types (Real, Integer, boolean and one-dimensional arrays)
Data flow (parameter passing)

2. String Operations (Concatenations and substrings)
String operations can process string data. String operations include:
Concatenations
Sub-String
Concatenation
Concatenations is joining two strings. Two strings in and one string out.
Example:
PRINT “House” & “boat”
Result:
Houseboat

3. Need to know coding for exam
Sub-String
Selecting parts of string. VB uses Mid$ to extract a substring from a string.
Example 1:
“Hello higher Class” – Input string
Mid$(string_in, 1, 1)
Result:
“H”
Example 2:
“I made him an offer he could not refuse”
Mid$(string_in, 3, 8)
“Made him” – starting at position 3 and counting 8 characters
Need to know coding for exam

4. Formatting Input/output
The way the program displays the data on the screen when inputting and outputting.
Input Methods for VB
Input box
Text box
Output Methods for VB
Message box
Picture box
List box
Tab() function can be used to create tabs in the output program.

5. Three basic control constructs used to define the order in which the instructions in a program are executed. These control constructs are found in all classifications of programming languages to control the flow of execution of the program code.
Control Structured programming is based on three constructs:
sequence
selection
repetition
Sequence
Order in which you give instructions to the computer. In sequence, one instruction is executed after another.
The purpose of sequence is to ensure that instructions given to the computer are executed in the correct order.

6. Example
Algorithm to add two numbers
Ask user for first number
Take in first name
Ask user for second number
Take in second number
Add two numbers to find total
Display total
This would work only if the steps are followed.
What would happen if this was used?

7. Selection
Based on one or more condition, used together with a control structure such as IF or CASE. Conditions have values, they are either true or false.
The purpose of selection is to allow a choice to be made in a program.
Common control structures:
If Mark >= 50 THEN
Picdisplay.print “Pass”
Else
Picdisplay.print “Fail”
End if
Select Case Mark
Case Mark >= 50
Picdisplay.print “Pass”
Case Mark < 49
Picdisplay.print “Fail”
End Select

8. Control Structured programming is based on three constructs:
sequence
selection
repetition
Repetition
Involves using loops. Loops may be either conditional or Unconditional (Fixed)
The purpose of repetition is to allows statements in a program to be repeated as many times as is necessary.  

9. Types of Loops
Unconditional Loops (Fixed Loops)
Repeat a set of program statements for predetermined number of times.
Fixed loops are controlled by a variable called a loop counter.
Example:
FOR counter equal starts number TO finish number
Do something
NEXT

10. Repeats instructions until a condition is satisfied. Advantage
Conditional Loop
Repeats instructions until a condition is satisfied.
Advantage
Amount of data to be processed need not be known in advance
A mathematical calculation can continue until answered
Example Do
mark1 = InputBox("Please enter mark 1")
If mark1 > 10 Or mark1 < 0 Then
MsgBox ("Please enter a mark between 1 and 10")
End If
Loop Until mark1 >= 0 And mark1 <= 10

11. 42 Mark Data Storage Variables
Data is stored in a computers memory in storage locations. Each storage location in the computers memory has a unique address.
By using variable names a programmer can store, retrieve and handle data without knowing what the data will be.
Types of variables
Local
Global
Mark
Dim Mark as Integer 42

12. Global Variables
Can be referred to from anywhere in a program.
Can be changed by any subprogram in the program.
Modern programming practice recommends against the excessive use of global variables. They can lead to poor program structure, and tend to clog up the available name space.
Local Variables
Only exists within the subprogram in which it is declared. Will not be recognised by any other subprogram.
Scope of variables
The variable the sub program is used in. There is no need to worry about having the similar variable names when using different sub programs, since they cannot have any effect outside their scope.

13. Data Type
String – may include letters, digits and punctuations.
Integer – may consist of whole numbers
Single/Real – may consist of whole number and real numbers (fractional)
Boolean – may have two values, true or false.

14. Structured Data Types
Related data items can be stored together using arrays.
A data structure is a way of storing data in a computer in an organised way. One of the simplest data structures used in computer programming is called an array and is an example of a static data structure because it is of a fixed size within memory as defined within the structure of the program.
Array
A set of data items of the same type grouped together using a single variable name.
Allows program to be more reliable and efficient.
Example
Wanted a program to take in 20 names and 20 test marks. Without an array you would need to declare 20 variables for name and 20 variables for mark.

15. Data Flow
The movement of data between subprograms is implemented by using parameters.
IN/OUT parameters
Variables that are changed or updated
IN parameters
Variables that only pass data into a subprogram.
OUT parameters
Variables which only pass data out of subprogram.
Parameters
Information about a data item being supplied to a subprogram (Function or procedure) when called into use.
When the sub-program is used this is known as parameter passing.

16. Parameters can be passed by either value or reference.
Deciding which method to use depends on whether the parameter is going into or in/out of a procedure.
By Value
When a parameter is passed into a procedure
When a parameter is passed by value into a subroutine, an exact copy of the current value of the variable is used. The value does not change.
Allows one-way transfer between the main program and the subroutines or functions.

17. By Reference
When a parameter is passed into a procedure, updated and passed back out again.
Two-way data transfer between the main program and the subroutine.
**Problem
Arrays are always passed byref when using visual basic programming.

18. Importance of Data flow
It is necessary to describe the data flow in a program in order to work out how the parameters should be passed between the main program and any subprograms.