Transcript Selection Part 2

Selection Part 2
Using Logical Operators, how
strings are compared and random
numbers
Logical Operators
• Logical operators are
used to create more
complex conditions
• They include AND,
OR and NOT
True AND True True
True AND False False
False AND False False
True OR
True True
True OR
False True
False OR
False False
NOT False True
NOT True False
Example Conditions
1=1 and 1=2 is false
2=3 or 2=2 is true
Not 1=2 is true
1<>1 and 4<9 is false
9=10 or 5>9 is false
4.6 >4 or 4.6>5 is true
Not true is false
Practical Example
Dim mark as single
Mark=txtMark.text
If mark >=70 and mark <80 then
messagebox.show(“You have a B!”)
End if
Practical Example #2
Dim number as integer
Messagebox.show(“I have 2 numbers between 1
and 10. Can you guess one of them?”)
Number=txtGuess.text
If number = 3 or number=8 then
messagebox.show(“Correct”)
Else
messagebox.show(“Wrong! Guess again!”)
End if
Comparing Strings
• Every character has a different ascii
number associated with it
• Example: a 97, b 98, c 99 etc.
A 65, B 66, C 67
– Notice that capitals have a lower ascii value
than lowercase letters
– As result “Apple” is less than “apple”
Comparing Strings con’t.
“dog” = “dog” is true
“cat = “ Cat” is false
“elephant” < “Zebra” is false
“abcd” > “Abcd”
“abc” < “abcd”
Practical Example
Dim user, password as string
User=txtUser.text
Password=txtPassword.text
If user=“krnic” and password=“computers” then
Messagebox.show(“User validated. Key Unlocked!!!!”)
End if
Practical Example #2
Dim person as string
Person=txtName.text
Messagebox.show(“Please enter your name is lowercase
letters.”)
If person >=“m” then
Messagebox.show(“You belong in the second half of the
list”)
Else
Messagebox.show(“You belong in the first half of the
list.”)
End if
Randomizing Numbers
• Random numbers are often used to mimic
behaviours in computer programs
• For example, consider playing against a
computer in a game of cards
• By randomizing a number between 1 and
4 you could get the computer to act as if it
is deciding which of its four cards it will
give up
Functions
• A function generates/returns a value
• To create a random number we can use a
pre-built function called rnd()
• To use this we must first use the
randomize statement in the event where
we want to use the rnd() function
• The rnd() function will generate a random
number between 0.0000 and 0.9999
RND() con’t….
• By generating a random number between 0.0000 and
0.9999 we can use some math to make a random
number generator that includes any range of numbers
• Here’s the formula:
Math.round(min + rnd()* range)
For example: if we want a random number from 1 to 4 our
code would look as follows:
Math.round(1+rnd()*3)
Of course we should first create a variable and assign to it our number
Dim number as integer
Number=Math.round(1+rnd()*3)
Practice
What is the line of code that would generate
the following random range of numbers:
1 to 10
20 to 30
-5 to 2
-3 to 10
100 to 1000
Practical Example
randomize
Dim number, playerGuess as integer
Number=math.round(1 +rnd()*99)
lblPrompt.text=“I have a number between 1 and 100. Can
you guess it??”
playerGuess=txtGuess.text
If payerGuess=Number then
messagebox.show(“Correct!”)
Else
messagebox.show(“Sorry but your guess was
incorrect!”)
End if
Exercises
1. Create a program
that allows a user to
click a button that
then places in a
textbox a random
number from 1 to 10.
Exercise 2
2. Create a program that allows a user to
guess a number selected randomly by
the computer. The number is to be
between 1 and 100. Make sure you
assign the computer’s random number
to a variable in the load event of the
form otherwise each time the player
presses the button to check the
number a new one will be generated.
Exercise #3
• 3. Create a program that
allows a user to randomly
relocate a red label on a form.
Relocation occurs upon the
click of a button. In order to do
this you will need to determine
the width and height of the
form and then randomize
numbers in these ranges i.e. 1
to formWidth and 1 to
formHeight. You can change
the location of the label by
assigning new values to its left
and top properties.