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NOTES FOR VISUAL BASIC PART 1

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1.Introduction to vb

What is vb?

vb is a user friendly event driven and partly objected oriented programming language using which we can develop:

database application.

web enabled application.

and variety of other window based application.

Who developed vb?

vb is developed by Microsoft in 1991 as Visual Basic 1.0.

Why vb was developed?

before vb window based application was being done using c and window based compiler which was a slow and tedious process. it required lots of coding. to speed up development of window based application vc++ and Microsoft foundation class were developed. but the development process was still tedious and slow. to boost development of window based application easily and fastly vb was introduced.

What are the different editions of vb?

there are three editions of vb:-

standard or learning edition: contains basic language feature and tools.

professional edition: contains more feature and tools when compared to standard edition.

enterprise edition: contains most advance feature and tools.

the edition which we are using is enterprise edition.

What are the hardware requirement to use vb?

http://www.google.com/url?q=http%3A%2F%2Fcarrierascent.com%2Fnotes_page%2Fnotes_page.htm&sa=D&sntz=1&usg=AFQjCNGlL2S_sNgVSz8N5-CIr6n3n37p5w

the hardware requirement are as follows:

cd-rom drive

cd-rom (1 to 7 cds). first cd rom contains compilers for various languages like vb, vc++, visual foxpro, visual internet developer etc. remaining cds contains help, client server tools, samples etc.

windows 9x Os.

80 to 120 mb for installation of vb.

40 mb free hard disk space for user generated program.

16 mb ram minimum ( 32 mb ram recommended)

80486 based micro processor ( Pentium 166 mhz recommended)

What is Event Driven programming?

when a program consists of one or more than one event procedures and those procedures accomplish the task to be done by program it is know as event driven programming.

What is event?

Event is any action performed by either performed by user or performed by program itself. for example mouse-click, key press, window resize etc.

What is the difference between structured/procedure oriented and event driven programming

Structured/Procedure Oriented Event Driven Programming

Program consists of one or more procedure. Program consists of one or more event

procedure.

Programming task is completed by

procedure.

Programming task is completed by event

procedure.

The order of execution of procedure is more

or less predictable.

The order of execution of event procedure

depends on user performed action.

Procedure oriented programming is not

suitable for window based application.

Event driven programming is suitable for

window based application.

What do you mean by IDE ?

Ide stands for integrated development environment. it is collection of program allowing to compose and edit the program, test the program, run the program and debug the program.

Describe working environment of vb?

Working environment of vb is compsed of many elements:

title bar: where program title, project name and program mode is displayed

menu bar: contains menu and related commands.

tool bar: consists of icons which are short cuts to frequently used commands some toolbars are : standard, formatting etc.

toolbox: on the left side toolbox appears which contains controls.

form designer: appears in middle where graphical user interface element(controls) are placed.

properties window: using this we can set properties of controls.

project explorer window: displays files which make up the project

form layout window: displays form-icon used to set start up position of form.

immediate window: useful to test any statement or to print value of variable.

What are the different modes of vb program?

there are three modes of vb program:

design: ( when designing form and writing code)

run : when a program is running.

break: when any occurred in program.

What is project file? why it is needed?

project file contains information about all those file which make the project. it stores location of individual file with path. when saving project it saves all files one by one inside project. when we open project it automatically opens all files which are part of project we need not to open each file one by one thus saving time. project file has extension “vbp”.

What is executable file. how it is made?

to make executable file (exe) we have to go to file menu and have to select make exe.

copying of exe file to another computer and running the exe file does not guarantee that the executable file will run there because a window based program depends on many different file. it better to run distributable package using package and deployment wizard.

What is module?

module is collection of procedures and functions corresponding to a file in disk will generate. benefits are:

it provides code reusability and shariblity.

avoids code repetition.

testing and debugging becomes easier.

type of module:

form module: normally contains event procedures, other procedure and function which will be used inside the same form module. extension is .frm

basic module: normally contains global variables, procedure and function which can be accessed across other modules. extension is .bas

class module: contains definition of class, member function and properties. extension is .cls

How to use code editor window?

code editor window can be brought forward using either of these methods:

select view-> view code

right click on form and select view code

double click on any control or on double click on form.

from project explorer window select the form name and click on button view code.

navigation of code editor window:

control+left arrow : move one word left

control+right arrow : move one word right

control +home : move to beginning of code view

control +end : move to end of code view

home : move to beginning of line

end : move to end of line

control+up arrow : move one procedure up

control+down arrow : move one procedure down

shift+f2: view definition of function or procedure under cursor

control+shift+f2: go to last position of cursor

what is documentation? why it is needed?

documention of code is very necessary. using documention we can increase readability of our program. using documentation we can store addition information like:

date and time of program

version no. of program

company for which it was created

author of the code

variables used and purpose

algorithm of program

explaination of statment

documentation makes the program easily understable. in future if we are going to make modification in program it will help greatly. we use ‘(apostrophe) to write comments or rem keyword.

how formatting of code is done?

formatting of code make program easy to read. indentation makes easy to follow closing of control structure. different background and foreground colors, fonts, font size can be assigned to normal text, keywords etc. using tool->options->editor format tab. procedure seperator line can also be turned on to help to identify where one procedure is beginning and ending.

describe environment options in vb?

select tools->options->environment tab

under when visual basic starts

if option button selected is prompt for project: each time visual basic starts a dialog box appears which lets us select type of project.

if option button selected create default project: each time visual basic starts it automatically open standard exe project.

under a program starts:

if save changes: is selected when program is about to start it saves the changes

made in project.

if selected prompt to save changes: is selected when program is about to start it will ask to save the changes.

if selected don’t save changes: it will not save the changes made in project and will run program.

show templates for: we can have many templates available for use as starting point for form, mdi forms, modules etc.

Describe editor options.

select tools->options->editor tab.

auto syntax check: if checked , when writing a statement and pressing enter check the statement for error.

require variable declaration: puts ‘option explicit’ statement in module’s general declaration section which forces declaration of variable before use as in c-language.

auto list member: if checked gives popup list consisting of properties, methods supported by object.

auto quick info.: if checked gives information about function parameter and data type of parameter which current function will work on.

auto data tips: if checked gives list of constant which can be assigned to a variable or to parameter of a procedure or function.

dim b as Boolean

type b= then you will get true, false in a list

auto indent: if checked starts new line just below the previous line.

tab width: specify the amount of space generated by a tab key.

drag and drop text editing: if checked supports drag and drop in code editor window.

default to full module view: if not checked only one procedure will be visible at a time.

procedure separator: if checked draws line among procedures.

Describe automatic code completion feature of vb.

when we have to use any object property or any method of object we have to type just a few letter of that property or method as soon as the property or method is selected from popup list we can press control+space key combination to complete the whole property or method thus saving key stroke.

2. Creating programs

What is Object?

object is class variable which is composition of properties, methods and data member. object is fundamental requirement of any object oriented language. object has three characteristics:

state: state of any object it defines identity of object.

behaviour: behaviour of any object is decided by member functions(methods) to which object can respond.

method: it is also known as member function it performs computation on data member or any kind of action.

What is property?

property of any object is actually member procedure which allows to set value in data member ( working as mutator) or allows to retrieve value of data member ( working as accessor).

How to create program in vb?

steps are as follows:

first decide the controls which will be used to create graphical user interface.

set properties of controls

write event procedure coding.

How to get print of visual basic program.

save the project

select file->print

from the dialog box specify:

under range:

selection – to print selected code

current module- to print current module

current project- to print all modules in current project

under print what:

form image- to print the image of form.

code- to print code

form as text- to print form as text format , resulting of printing of controls along with properties and code

under setup, specify paper size, orientation of paper and printer to use

Describe controlling objects. or describe toolbox.

control depend on interface which are properties,events and methods.

normally there are many controls found in visual basic. some controls are activex controls which can be included in toolbox using project->component dialog. there are some control already available in toolbox which are also known as intrinsic controls or standard controls. description of standard controls are as follows:

label control: it is useful to give user a prompt.

text box: it is useful to input/output data for program.

list box: it is useful to give list of items and user can select items from list.

combo box: it is combination of text box and list box user can type new item or can select an existing item from combo box list portion.

image box: can display picture

picture box: can display picture.

directory , drive and file list box: allows to create a dialog box to save , open file

ole control: allows to use feature of other existing application.

data control: useful to write data base program

option button or radio button : allows to select only one of several available choices.

check box: allows to select many choices of several available choices.

frame: acts as container to place related controls together.

command button or push button: useful to confirm action like close, open, apply etc.

timer: useful to execute certain piece of code after specified interval. default property is enabled which takes true or false value.

shape: useful to decorate form

line : useful to draw line to decorate form

scrollbar: useful to take input/output or scrolling data.

3.Variables Procedures

What is variable?

variable is name given to computer memory location where we can store value and retrieve the stored value by name.

variable is fundamental requirement of any programming language.

rule of naming variable or identifier:

variable name must start with alphabet.

later on digits can be used, under score can also appear.

variable name is not case sensitive

only a-z, 0-9 and _ can appear in variable Name

space and special are not allowed.

variable name must not match with keyword

we can have variable name 255 characters long

name of control must not exceed 40 characters

What is data type?

data type of variable defines range, memory and valid operation for a variable

Data type Range Memory

1.Byte 0 , 255 1

2.Integer % 32767 , 0 , -32768 2

3.Single ! +/- 3.4 e +34 4

4.Double # +/- 1.7 e+308 8

5.Date 1-1-100 to 31-12-9999 8

6.string(variable) $ 2 billion characters

6.string(fixed) $

7.boolean True, false 2

8.object Reference of any object

9. variant Range for number is same as

double

Range for string is same as 2

billion characters

How to declare variable?

(a) dim x as integer, y as integer

or

dim x%,y%

(b) dim x, y as integer

then x will be variant and y will be integer

(c) dim b as Boolean

Describe scope of variable.

scope specifies the code range where value of variable is accessible.

local variable: accessible inside a function or procedure. we use dim keyword to declare local variable.

module level global variable: accessible inside a module but not outside from other module. we use dim or private keyword to declare module level global variable and declare it inside general declaration of module.

global variable : accessible from every where. we use public or global keyword to declare global variable inside general declaration of module.

What do you mean by shadowing of variable?

if global variable or module level global variable exists with name ‘a’ and a local variable also exists in a procedure or function it prevents accessing of global or module level global variable because local variable is given preference. to

access value of global variable we can use

modulename.globalvariable e.g. form1.a

what are the operators in vb?

arithmetic operator:

+ for addition,

- for subtraction.

* for multiplication

\ for integer division c=10\3 c will be 3

/ for float division c= 10/3 c will be 3.333

^ for power e.g. c=10^3 therefore c will be 1000

mod for modulo division c=10 mod 3 c will be 1

relation operator

>,>=,<,<=,=, <>

3. logical operator

and, or, not

assignment

=

4 .Controlling program Execution

Why do we need control structure?

We all need to alter our action depending on changing circumstances. For example If weather is fine I will go Dongargarh on bike otherwise I will go by train. In the same way ‘vb’ language too must be able to perform different action under one condition and different action under another condition and this is made possible by control structure. Sometimes a given set of statements are needed to run repeatedly this is done using loop control structure.

Write notes on if control structure./ explain branching structure in vb./ write short notes on if statement/ write short note on select case.. end select.

The general form of if statement is:

(a)if-endif statement

the general format of if statement is

if (condition is true) then

execute this statement

end if

The keyword if tells the compiler that what follows, is a decision control instruction. The condition following the keyword if is optionally enclosed within a pair of parentheses. If the condition, whatever it is, is true, then the statement is executed. If the condition is not true then the statement is not executed; instead the program skips past it.

(b) if –else-endif statement

if statement by itself can execute only one statement if condition is true. If it required running a group of statements when condition is true we have to enclose those statements inside curly brace known as compound statement. The above form of if statement mentioned in (a) will not do anything when condition is false. If we want to run statement when condition is false we need if-else construct.

General format of if-else construct is

If (condition is true) then

Execute this statement

Else

Execute this statement if condition is false

end if

Condition is specified using relational operator

x= y means x is equal to y.

x<>y means x is not equal to y.

x< y means x is less than y.

x>y means x is greater than y.

x<=y means x is less than or equal to y.

x>=y means x is greater than or equal to y

What is the use of logical operator?/what is meant by logical testing?

Logical operator and, or, not are useful to join more than one condition whereas not operator negates meaning of condition. these are required in following situations:

* When it is be tested whether a value falls within a particular range or not.

* When after testing several conditions the outcome is either true or false.

* Reverse the logic of condition using ‘not’ logical operator.

control structure mostly depend on logical testing to perform some piece of code either selectively or repeatedly.

What are the different forms of if –else statements?

Different forms of if-else statement are as follows:

1. if (condition) then

do this

and this

end if


do this

do this

else

do this

do this

end if

3. if (condition) then single-true statement

4. if (condition) then single-true statement else single-false-statement


if (condition) then

statement

else

statement

end if

else

if (condition) then

statements

else

statements

end if

end if

if condition then

statements

elseif condition then

statements

elseif condition then

statements

else

statements

end if

program to find division given percentage

Private Sub Command1_Click()

Dim a!, b$

a = Text1.Text

If a < 33 Then

b = "fail"

Else

If a < 45 Then

b = "third"

Else

If a < 60 Then

b = "second"

Else

b = "first"

End If

End If

End If

Text2 = b

End Sub

place label : having caption enter percentage

place text1: having text property cleared

place label2 : having caption division


place command1: having caption find division

program to check leap year


Dim a%

a = Text1

If a Mod 100 = 0 Then

If a Mod 400 = 0 Then

Text2 = "leap"

Else

Text2 = "not leap"

End If

else

If a Mod 4 = 0 Then

Text2 = "leap"

Else

Text2 = "not leap"

End If

End If

End Sub

place label : having caption enter year


place label2 : having caption result of testing


place command1: having caption check for leap year

program to print message teenage, child, old etc. according to given age


Dim a!

a = Text1

Select Case (a)

Case Is <= 8

Text2 = "child"

Case 9 To 14

Text2 = "teenager"

Case 15 To 20

Text2 = "young"

Case 21 To 28

Text2 = "adult"

Case Is > 28

Text2 = "old"

End Select

End Sub

place label : having caption enter age


place label2 : having caption state


place command1: having caption check age

State the difference between select case and if

select-case

1.All programs made using select-case can

be solved using if. select case takes

different action depending on value of a

single variable.

2. ‘select-case’ leads to more structured

programming and level of indentation is

manageable even if we have nested

select-case.

if-else

All programs made by ‘if’ are not possible to

solve by ‘select-case’.

‘if’ leads to less structured programming

and level of indentation is difficult to

manage if using nested ‘ifs’.

Multiple if

1.multiple ‘if..else’ contains more than one

end if. Each ‘end if’ corresponds to each ‘if’.

2. multiple if requires more comparison.

Therefore it is not efficient.

Nested if..else

1.nested ‘if..else’ contains more than one

‘else if’ but just one ‘end if’..

2. nested if requires less comparison.

Therefore it is efficient.

Write short notes on goto statement and its limitations.

‘goto’ is a statement which is quite common in monolithic programming paradigm. some languages like basic, fortran etc. use it deliberately. using goto we can do :

skipping of some statement without executing them.

transferring of control to a labeled statement.

coming out of loop whatever level of nesting of loop may be.

note that break statement can take out of loop inside which it lies but goto statement can take out of loops irrespective of level of nesting of loops.

different type of goto can be:

conditional-goto : if it is used with ‘if’ statement.

unconditional-goto : if it is not used with ‘if’ statement.

limitations of goto: unwise use of goto make it difficult to trace logic flow of program and makes it difficult to remove logical error of program therefore, as far as possible, we must avoid use of goto.

program to print 1 to 10 using goto statement


Dim a%, b%, c%, t$

a = Text1

b = Text2

c = Text3

mm: t = t & a & " "

a = a + c

If a <= b Then GoTo mm

Text4 = t

End Sub

place label1 : having caption enter starting term


place label2 : having caption enter stopping term


place label3: having caption enter value to step by



place command1: having caption print series in text box

Why loop control structure is needed?

Without loops we execute the same series of actions, in the same way, exactly once. Loops allows to execute same portion of program code repeatedly a specified no. of times or until a particular condition is being satisfied. This repetitive operation is done through a loop control structure.

There are four methods using which we can repeat a part of a program which are:

* for statement

* while statement

* do-while statement

* goto statement (not recommended)

Write short notes on ‘while’ (entry level control structure/test and do) loop.

In programming we require to execute same set of instructions a fixed number of times. E.g. we want to calculate gross salary of ten different persons, we want to convert temperatures from centigrade to Fahrenheit for 15 different cities. The ‘while’ loop is suited for this.

‘ program to print 1 to 10 on form

private sub command1_click()

dim a%

a=1

do while a<=10

print a

a=a+1

loop

end sub

General format is

1.

initialize loop counter

do while(condition is true)

do this;

increment loop counter;

loop

Write short notes on ‘while’ (entry level control structure/test and do) loop.

In programming we require to execute same set of instructions a fixed number of times. E.g. we want to calculate gross salary of ten different persons, we want to convert temperatures from centigrade to Fahrenheit for 15 different cities. The ‘while’ loop is suited for this.

‘ program to print 1 to 10 on form

private sub command1_click()

dim a%

a=1

do

print a

a=a+1

loop while a<=10

end sub

General format is


do

do this

increment loop counter

loop while(condition is true)

Differentiate between while/while..wend and do-while loop.

Body of loop in case of ‘while’ loop will not execute even once if condition of while loop is false but in case of ‘do-while’ loop body of loop will run at least once because condition is tested at the end of loop body.

format of do..loop is


do

do this


loop while(condition is true)

format of while loop:


while condition

do this


loop

format of while.. wend loop:


while condition

do this


wend

Do while loop must test a condition that will eventually become false, otherwise the loop would be executed forever, indefinitely known as infinite or indefinite loop.

while loop or while..wend loop test condition and if condition is true then statements are executed if condition is false statements are not executed even once.

do.. while loop test condition later therefore if condition is false statements are executed at least once.

while..wend statement can not use ‘exit do’ statement to come out of loop whereas do..while and do..loop…while can use ‘exit do’ statement to come out of loop.

Write short notes on for loop.

‘for’ loop is most popular loop. ‘for’ loop allows us to specify three things about a loop in a single line which are:

1. Setting a loop counter to initial value.

2. Testing the loop counter to determine whether its value has reached the number of repetitions desired.

3. Increasing the value of loop counter each time the program segment within the loop have been executed.

The general format of for statement is as us under:

for variable= intialvalue to endvalue step stepvalue

do this

and this

and this

next

Write short notes on odd loop.

The loops in which no. of times statements inside loop body will execute are known as finite or determinate loop. The loops which will never terminate execution of statements inside loop body are known as infinite loop. The loop about which we are not certain how many times statements inside loop body will execute but we are sure that it will terminate after some time is known as odd loop.

Write program to demonstrate loops to solve Fibonacci series up to n terms.


Dim i%, term1&, term2&, term3&, t$, nterms

term1 = 0

term2 = 1

nterms = Text1

' method A- using for loop

‘For i = 1 To nterms

't = t & term1 & " "

'term3 = term1 + term2

'term1 = term2

'term2 = term3

'Next

‘method B-using do-while…loop

'i = 1

'Do While i <= nterms ' do loop until i>nterms

't = t & term1 & " "


'term1 = term2

'term2 = term3

'i = i + 1

'Loop

‘ method C- using do…loop while

'i = 1

'Do

't = t & term1 & " "


'term1 = term2

'term2 = term3

'i = i + 1

'Loop While i <= nterms ' loop while until>nterms

‘method D-using while … wend

i = 1

While i <= nterms

t = t & term1 & " "

term3 = term1 + term2

term1 = term2

term2 = term3

i = i + 1

Wend

Text2 = t ‘series will go into a text box

End Sub

place label1 : having caption enter no. of terms of Fibonacci series


place label2 : having caption series is


Write short Notes on ‘exit do / exit for’ in Loop/write program to check primality.

We often come across situations when we want to jump out of a loop instantly, without waiting to get back to the conditional test. The keyword ‘exit do / exit for’ allows us to do this. When the keyword ‘‘exit do / exit for’’ is encountered inside any loop statement, control automatically passed to the first statement after the loop. An ‘exit do / exit for’ is usually associated with an ‘if’ statement applicable to loop.

The keyword ‘exit do / exit for’ takes the control out of the loop inside which it is placed.

What is use of const keyword?

const keyword is useful to declare a constant with a given symbolic name whose value can not change during program run time.

const pi =3.1415

What do you mean by nested loop?

nested loop is a special case in which one loop contains other loop inside its loop body. for each value of outer loop counter , inner loop counter changes frequently.

program to print prime series between 1 to 100 using for loop and exit for


Dim a%, b%, c%, n%, t$, i%

a = 1

b = 100

For n = a To b

For i = 2 To n - 1

If n Mod i = 0 Then

Exit For

End If

Next

If i >= n Then

t = t & " " & n

End If

Next

Text1 = t

End Sub

place label1 : having caption set to prime series is



Define Array.

Array or Subscripted variables:

Array is collection of variables having common name and common data type. Individual variable in collection is identified by index or subscript. Elements of array occupy contiguous memory location.

How can we declare a single dimension Array?

Declaration (single dimension numeric array):

dim a(5) as integer

or

dim a%(5)

‘a’ is name of array.

it means there are 6 variables viz. a(0),a(1),a(2),a(3),a(4),a(5) index or subscript will ange from 0 to 5. All variables will be integers.

dim b!(10)

or

dim b(10) as single

It means there are 11 variables viz. b(0),b(1)… b(5) index or subscript will change from 0 to 10. All variables will be single.

How we can initalise an array?

Initialization of array is not supported by vb.

What are the usages/Applications of Array?

Application of arrays:

* It is useful to solve simultaneous equation.

* It is useful to solve problems of data structure like searching, sorting, linked list, graph etc.

* Its is useful to solve such problems requiring variable of same data type in contiguous memory location.

What is Multi Dimension Arrays? What are their usages?

Array declared with more than one dimension is known as multi-dimension array.

Often multi dimension array is needed to store data for table and matrices. Multi -dimension array has more than one subscript. Two dimension array contains two subscript, three dimension array has three subscript and so on.

program to add two matrix of order 3x3

place three command buttons on form labeled input, sort, print

Dim a%(2, 2), b%(2, 2), c%(2, 2), i%, j%


MsgBox "enter value for array a"

For i = 0 To 2

For j = 0 To 2

a(i, j) = InputBox("enter value")

Next

Next

MsgBox "enter value for array b"

For i = 0 To 2

For j = 0 To 2

b(i, j) = InputBox("enter value")

Next

Next

End Sub


For i = 0 To 2

For j = 0 To 2

c(i, j) = a(i, j) + b(i, j)

Next

Next

End Sub


For i = 0 To 2

For j = 0 To 2

Print c(i, j) & " ";

Next

Print

Next

End Sub

Program to sort a given array

place three command buttons on form labeled input,add,print

Dim a%(4)


Dim i%

For i = 0 To 4

a(i) = InputBox("enter value", "data entry", 1)

Next

End Sub


Dim i%, j%

For i = 0 To 3

For j = 0 To 3 - i

If a(j) > a(j + 1) Then

t = a(j)

a(j) = a(j + 1)

a(j + 1) = t

End If

Next

Next

End Sub


Dim i%

For i = 0 To 4

Print a(i)

Next

End Sub

What is dynamic array?

dynamic array is an array whose no. of elements are not specified earlier. no. of elements can be requested from user at program run time. redim keyword can be used to allocate memory for such no. of elements. after allocating memory we can store value in elements of array.

dynamic array saves memory because we have to allocate memory for such many elements which we want to use.

Program to sort an array using dynamic array

Dim a%(), n 'note element is not specified


Dim i%

' take no. of elements required

n = InputBox("enter no. of elements")

'allocate memory

ReDim a(n - 1) ' workout

For i = LBound(a) To UBound(a)

a(i) = InputBox("enter value", "data entry", 1)

Next

End Sub


Dim i%, j%

For i = LBound(a) To UBound(a) - 1

For j = LBound(a) To UBound(a) - 1 - i

If a(j) > a(j + 1) Then

t = a(j)

a(j) = a(j + 1)

a(j + 1) = t

End If

Next

Next

End Sub


Dim i%

For i = LBound(a) To UBound(a)

Print a(i)

Next

End Sub

place command1:having caption set to input

place command1:having caption set to sort

place command1:having caption set to print

Program to add two matrix using non-dynamic array.

Dim a%(2, 2), b%(2, 2), c%(2, 2), i%, j%,t$


MsgBox "enter value for array a"

For i = 0 To 2

For j = 0 To 2


Next

Next

MsgBox "enter value for array b"

For i = 0 To 2

For j = 0 To 2


Next

Next

End Sub


For i = 0 To 2

For j = 0 To 2

c(i, j) = a(i, j) + b(i, j)

Next

Next

End Sub


For i = 0 To 2

For j = 0 To 2

t=t & c(i, j) & " "

Next

t=t & vbcrlf

Next

End Sub


place command1:having caption set to add

7place text1: having multiline property true and scrollbars set to 2 for both


Program to multiply two matrix using dynamic array.

Dim a%(), b%(), c%(), i%, j%, m%, n%, p%, q%


m = InputBox("enter no of rows in matrix a")

n = InputBox("enter no. of columns in matrix a")

p = InputBox("enter no of rows in matrix b")

q = InputBox("enter no. of columns in matrix b")

If n <> p Then

MsgBox "invalid matrix order for multiplication"

Exit Sub ' come out of event

End If

MsgBox "enter value" & m * n & " for array a"

ReDim a(m - 1, n - 1) 'allocate memory before storing value

For i = LBound(a, 1) To UBound(a, 1)

For j = LBound(a, 2) To UBound(a, 2)


Next

Next

MsgBox "enter value" & p * q & " for array b"

ReDim b(p - 1, q - 1) 'allocate memory before storing value

For i = LBound(b, 1) To UBound(b, 1)

For j = LBound(b, 2) To UBound(b, 2)


Next

Next

End Sub


ReDim c(m - 1, q - 1)

For i = LBound(a, 1) To UBound(a, 1)

For k = LBound(b, 2) To UBound(b, 2)

c(i, k) = 0

For j = LBound(a, 2) To UBound(a, 2)

c(i, k) = c(i, k) + a(i, j) * b(j, k)

Next

Next

Next

End Sub


For i = LBound(c, 1) To UBound(c, 1)

For j = LBound(c, 2) To UBound(c, 2)

Print c(i, j) & " ";

Next

Print

Next

End Sub


place command1:having caption set to multiply


what is use of preserve keyword?

preserve keyword is useful to let the dynamic array remember the older contents it has.

e.g.


Dim a%()

'redimension

ReDim a(2)

a(0) = 10

a(1) = 20

a(2) = 30

Print a(0), a(1), a(2)

'resize array without using redim

ReDim a(3)

a(3) = 40

Print a(0), a(1), a(2), a(3)

End Sub


Dim a%()

'redimension

ReDim a(2)

a(0) = 10

a(1) = 20

a(2) = 30

Print a(0), a(1), a(2)

'change array size and use preserve

ReDim Preserve a(3)

a(3) = 40

Print a(0), a(1), a(2), a(3)

End Sub

place command1:having caption set to test without preserve

place command1:having caption set to test with preserve

What is function?

a number of statements grouped into a single logical unit is referred to as a function which returns a value and which is made to complete a specific task. A program can be made of many functions.

Types of functions:

User defined function: these are those functions which are made by programmer for his programming convenience.

Library function: these are those functions which are readymade and are provided by compiler, uses of which are possible by including corresponding header files. Source code of library function is not available to programmer but its object codes are available in precompiled form.

What is procedure?

a number of statements grouped into a single logical unit is referred to as a procedure or subroutine which does not return any value and which is made to complete a specific task. A program can be made of many procedures.

What are the usages/applications of functions/procedures?

Usages are as follows:

Function/procedure avoids code repetition:- once a function/procedure has been made we can call the function/procedure to complete the task when and where necessary.

Function/procedure used carefully makes the process of error removing easier called debugging.

Once function/procedure is tested and satisfies the one’s needs, one can convert it in to library, and can distribute it others for use.

Function/procedure allows breaking bigger task into smaller manageable subtasks which is soul of modular programming.

Recursive function/procedure (function/procedure calling itself at least once) solves some typical programming tasks easily and with few lines of coding which otherwise would have taken several lines of code.

What do you mean by recursion?/what are recursive function explain with an example.

Expressing an entity in terms of itself is known as recursion. When function/procedure calls itself at least once the function/procedure is called recursive function/procedure. Recursive function/procedure contains a function/procedure call statement to call itself normally kept inside if-else construct. Putting function/procedure call inside if-else construct allows termination of recursive function/procedure call after some time.

While defining a recursive function/procedure we must take care of these two points

* Each time a function/procedure calls itself it must be closer, in some sense to a solution.

* There must be a decision criterion for stopping recursive function/procedure call otherwise it will execute till the stack overflows.

write program to find factorial using recursive function


Dim n%, m&

n = Text1

m = fact(n)

Text2 = m

End Sub

Private Function fact&(n As Integer)

If n <= 1 Then

fact = 1

Else

fact = n * fact(n - 1)

End If

user interface:

create a command button: having caption find factorial

create text1: having text property clear


create label1: having caption property set to enter a value

create label2: having caption property set to factorial is

write program to find factorial using function.


Dim n%, f&

n = Text1

f = fact(n)

Text2 = f

End Sub

'Private Function fact&(byref x%) ‘ by default calling by reference

'Dim i%, f&

'f = 1

'For i = 1 To x

' f = f * i

'Next

'fact = f

'End Function

Private Function fact&(ByVal x%)

Dim i%, f&

f = 1

For i = 1 To x

f = f * i

Next

fact = f

End Function

user interface:

create a command button: having caption find factorial



create label1: having caption property set to enter a value

create label2: having caption property set to factorial is

Explain call by value and call by reference

'when called routine is not able to change value of actual argument

'through dummy argument it is known as call by value


Dim a%, b%

a = Text1

b = Text2

swap a, b

'after call

Text5 = a

Text6 = b

End Sub

Private Sub swap(ByVal a%, ByVal b%)

'default is call by reference

Text3 = a

Text4 = b

Dim temp%

'interchange

temp = a

a = b

b = temp

End Sub

call by reference:

'when called routine is able to change value of actual argument

'through dummy argument it is known as call by reference


Dim a%, b%

a = Text1

b = Text2

swap a, b

'after call

Text5 = a

Text6 = b

End Sub

Private Sub swap(Byref a%, Byref b%)

'default is call by reference

Text3 = a

Text4 = b

Dim temp%

'interchange

temp = a

a = b

b = temp

End Sub

user interface:

6 textboxes: having text property clear and having default name text1,text2…

6 labels: having caption enter value of a, enter value of b, within called subroutine value of a, within called subroutine value of b, after call to swap value of a, after call to swap value of b

1 command button: having caption swap and having default name command1

PROVIDED BY. MR NAGENDRA DEWANGAN

NOTES FOR VISUAL BASIC PART 1 - Yola FOR VISUAL BASIC P… · NOTES FOR VISUAL BASIC PART 1 Back to...

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