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 TrueANDTrue ANDFalse ANDFalse TrueORTrue ORFalseTrue FalseORFalse NOTFalseTrue NOTTrueFalse

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 Example Conditions

Practical Example Dim mark as single Mark=txtMark.text If mark >=70 and mark <80 then messagebox.show(“You have a B!”) End if

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 Practical Example #2

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 and

RND() con’t…. By generating a random number between and 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 to to 2 -3 to 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.