Controlling Program Flow With Decision Structures

Controlling Program FlowWith Decision Structures

The If…Then Statement • Decision structures to control flow • True/False (boolean) decision structure • If a condition is true then certain statements will operate • If intGuess = 7 Then • Me.lblMessage.Text = “You guessed it” End If

The If…Then Statement • Many If…Then statements will use relational operators • = • < • < = • > • > = • < >

The If…Then…Else Statement • Else clause: evaluated when the If condition evaluates to false. • If intX = intSecret Then • Me.lblMessage.Text = “You Guessed it” Else Me.lblMessage.Text = “Try Again.” End If

Nested If…Then…Else Statements • When you have an If…Then decision structure within an If…Then decision structure

If…Then…ElseIf Statement • Used to decide between three or more actions

Select…Case Statement • Another decision structure • Sometimes preferred over the if…then…elseif

Select…Case Is Statement • Compares a range of values by using relational operators.

Random Numbers • Rnd generates random numbers • Equal to or greater than 0, less than 1 • (High – Low +1) * Rnd () + Low • Eliminate everything after the decimal Int • Randomize

Static Variables • Retains the value of a variable throughout program execution • Keep the scope as narrow as possible • Static intSecret As Integer

Algorithms • An algorithm states the code in words • Determine a secret number • Get a number from the player • Compare the number and the secret # • If higher than… • If lower than… • If equal… • Pseudocode: an algorithm with some code

Logical Operators • Joins two boolean expressions • Not, And, Or (order of operation) • If intGrade < 0 Or intGrade > 100 then • ‘out of range • If strItem = “book” And intquant > 10 then • ‘discount items over 10 • If Not strItem = “book” then • ‘done for every item except book me.radrock.checked

Message Box • Dialog box • Created by using its own statement MessageBox.Show(“display”, “title bar”) • Place anywhere you want a messagebox to appear

Counter Variables • A variable that is incremented by a constant number • Keeps track of number of guesses, button clicks, lives in a game • To increment a counter it is the counter = counter + constant intNumTries = intNumTries + 1 Test Grade

Checkbox Control • Prefix - chk • Similar to radio buttons • More than one may be selected • .checked property To do Menu

Controlling Program Flow With Decision Structures