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Objectives Include the selection structure in pseudocode and in a flowchart Write an If…Then…Else statement Write code that uses comparison operators and logical operators Create a variable having block scope Use the line continuation character Microsoft Visual Basic .NET: Reloaded

Objectives (continued) Concatenate strings Use the ControlChars NewLine constant Change the case of a string Determine whether an expression can be converted to a number Display a message in a message box Microsoft Visual Basic .NET: Reloaded

Objectives (continued) Include a nested selection structure in pseudocode, flowchart, and code Code an If/Elseif/Else selection structure Include a Case selection structure in pseudocode, flowchart and code Microsoft Visual Basic .NET: Reloaded

The Selection Structure Also called decision structure Make a comparison and choose between 2 paths depending upon the result of comparison (condition) Microsoft Visual Basic .NET: Reloaded

Writing Pseudocode for the If and If/Else Selection Structures If selection structure - 1 set of instructions which are processed if condition is true If/Else - 2 sets of instructions – the first when condition is true, the other when condition is false Microsoft Visual Basic .NET: Reloaded

Flowcharting the If and If/Else Selection Structures Microsoft Visual Basic .NET: Reloaded

Coding the If and If/Else Selection Structures Microsoft Visual Basic .NET: Reloaded

Coding the If and If/Else Selection Structures (continued) Statement Block Set of instructions in “true” path (between keywords If and Then) Optional set of instructions in “false” path (between keywords Then and End If) Any items in square brackets are optional Microsoft Visual Basic .NET: Reloaded

Comparison Operators Also referred to as relational operators Microsoft Visual Basic .NET: Reloaded

Comparison Operators (continued) Microsoft Visual Basic .NET: Reloaded

Using Comparison Operators – Example 1 Microsoft Visual Basic .NET: Reloaded

Using Comparison Operators – Example 1 (continued) Note: variable intTemp has block scope and can only be used in block in which declared Microsoft Visual Basic .NET: Reloaded

Using Comparison Operators – Example 1 (continued) Microsoft Visual Basic .NET: Reloaded

Using Comparison Operators – Example 1 (continued) Line continuation character Space followed by an underscore Used to break up long instructions onto 2 lines Concatenation Operator The ampersand ( & ) Used to concatenate (connect or link) strings Microsoft Visual Basic .NET: Reloaded

Using Comparison Operators – Example 1 (continued) Microsoft Visual Basic .NET: Reloaded

HOW TO… Microsoft Visual Basic .NET: Reloaded

Using Comparison Operators – Example 2 Microsoft Visual Basic .NET: Reloaded

Using Comparison Operators – Example 2 (continued) Microsoft Visual Basic .NET: Reloaded

Using Comparison Operators – Example 2 (continued) Microsoft Visual Basic .NET: Reloaded

Using the ToUpper and ToLower Methods Microsoft Visual Basic .NET: Reloaded

Using the ToUpper and ToLower Methods (continued) Microsoft Visual Basic .NET: Reloaded

Using the ToUpper and ToLower Methods (continued) Microsoft Visual Basic .NET: Reloaded

Logical Operators Microsoft Visual Basic .NET: Reloaded

Logical Operators (continued) Microsoft Visual Basic .NET: Reloaded

Truth Tables Microsoft Visual Basic .NET: Reloaded

Truth Tables (continued) Note: short-circuit evaluation can occur with “And” operator. Both conditions will not be tested if first condition tests false Microsoft Visual Basic .NET: Reloaded

Using the Truth Tables Understanding order of precedence is critical Microsoft Visual Basic .NET: Reloaded

Using the Truth Tables (continued) Microsoft Visual Basic .NET: Reloaded

Using Logical Operators in an If…Then…Else Statement Microsoft Visual Basic .NET: Reloaded

Modifying the Skate-Away Sales Application Microsoft Visual Basic .NET: Reloaded

Modifying the Skate-Away Sales Application (continued) Modify to eliminate unwanted error message Microsoft Visual Basic .NET: Reloaded

Modifying the Skate-Away Sales Application (continued) Microsoft Visual Basic .NET: Reloaded

The IsNumeric Function A predefined procedure that performs a specific task and returns a value after completing the task IsNumeric function checks if an expression can be converted to a number Returns Boolean true if able to convert to number Returns Boolean false if conversion cant be made Microsoft Visual Basic .NET: Reloaded

The IsNumeric Function (continued) Microsoft Visual Basic .NET: Reloaded

The MessageBox.Show method Microsoft Visual Basic .NET: Reloaded

The MessageBox.Show method (continued) Arguments in the MessageBox.Show method Text - a string containing the text to display Caption - text displayed in title bar Buttons - buttons to display in message box Can be one of 6 different constants Icon – icon displayed in title bar Defaultbutton – button automatically selected if user presses the Enter key on keyboard Microsoft Visual Basic .NET: Reloaded

The MessageBox.Show method (continued) Microsoft Visual Basic .NET: Reloaded

The MessageBox.Show method (continued) Microsoft Visual Basic .NET: Reloaded

HOW TO… Microsoft Visual Basic .NET: Reloaded

Nested Selection Structures When at least one side of the selection structure’s path contains another selection structure Inner structure is referred to as “nested” “Else” is paired up with nearest preceding If regardless of indentation of code Use when you want to make one decision and then choose between two options depending upon the result of the first decision Microsoft Visual Basic .NET: Reloaded

Nested Selection Structures (continued) Microsoft Visual Basic .NET: Reloaded

Nested Selection Structures (continued) Microsoft Visual Basic .NET: Reloaded

Nested Selection Structures (continued) Microsoft Visual Basic .NET: Reloaded

Nested Selection Structures (continued) Microsoft Visual Basic .NET: Reloaded

The If/ElseIf/Else Selection Structure Microsoft Visual Basic .NET: Reloaded

The Case Selection Structure PsuedoCode Get Grade Grade value: Display “Excellent” Display “Above Average” Display “Average” D,F Display “Below Average” Other Display “Error” Microsoft Visual Basic .NET: Reloaded

The Case Selection Structure (continued) Microsoft Visual Basic .NET: Reloaded

HOW TO… Microsoft Visual Basic .NET: Reloaded

Using To and Is in an ExpressionList To allows range of values in Case expression Example Number of items ordered Price per item 1-5 $25 6-10 $23 Is allows use of comparison operators More than 10 $20 Microsoft Visual Basic .NET: Reloaded

Using To and Is in an ExpressionList (continued) Microsoft Visual Basic .NET: Reloaded

Programming Example – Fat Calculator Application allows user to enter the total number of calories and grams of fat contained in a specific food Calculate and display 2 values: number of fat calories, and fat percentage Display appropriate message depending on level of fat percentage Microsoft Visual Basic .NET: Reloaded

TOE Chart Microsoft Visual Basic .NET: Reloaded

User Interface Microsoft Visual Basic .NET: Reloaded

Objects, Properties, and Settings Microsoft Visual Basic .NET: Reloaded

Objects, Properties, and Settings (continued) Microsoft Visual Basic .NET: Reloaded

Tab Order Microsoft Visual Basic .NET: Reloaded

Pseudocode btnExit Click event procedure close application btnCalc Click event procedure if the txtCalories and txtFatGrams controls contain numbers assign the numbers to variables calculate the fat calories by multiplying total calories by 9 calculate fat percentage by dividing fat by total calories display fat calories and fat percentage in appropriate labels if fat percentage is over 30% display “This food is high in fat” in message box else display “This food is not high in fat” in message box end if display “The calories and fat grams must be numbers” Microsoft Visual Basic .NET: Reloaded

Code Microsoft Visual Basic .NET: Reloaded

Code (continued) Microsoft Visual Basic .NET: Reloaded

Summary Selection structure allows program to make a decision and then select one of 2 paths depending upon the results of that decision Visual Basic .NET has 4 selection structures If If/Else If/ElseIf/Else Case Selection structures can be “nested” within other selection structures Outer structure contains primary decision Inner structure contains secondary decision Microsoft Visual Basic .NET: Reloaded

Summary (continued) All expressions in a selection structure evaluate to either true or false Use line continuation character (space &) to break up long instruction into 2 physical lines Use concatenation operator (&) to connect (link) 2 strings together String comparisons are case sensitive Use ToUpper and ToLower functions to convert case Microsoft Visual Basic .NET: Reloaded

Summary (continued) ControlChars.NewLine constant advances insertion point to the next line in a control Use logical operators to create compound conditions (And, Or, AndAlso) IsNumeric function verifies expression can be converted to a number MessageBox.Show allows communication with user in the form of a message box Use If/ElseIf/Else and Case selection structures to choose between multiple alternatives Microsoft Visual Basic .NET: Reloaded