Programing App Inventor

Variable Declaration App Inventor: Declare Variables using the “Define Variable As” Block – Find the Blocks Editor (top-left), click the Definition button, then pull out the correct block. – How would I make a variable named “count”???

Variable Assignment Assign a variable named “count” to 5 –In App Inventor, use “set global - to” block in the My Blocks Menu Only available once defined your variable Drag the “set global - to” block out Create a number block by typing in “5” in the editor window Click 5 into the “set global – to” block

App Inventor Math using Variables Combine the “Set-To” Block with operators from the “Built-In->Math” Menu Count = 9 Count = 5 Count = 14 Count = 3 Count = 1 (modulo gives the remainder of division)

Variable Initialization

You are forced to define a variables value when you declare it in App Inventor A general place for program initialization is the “When Screen1.Initialize” block – Note: Most Text-Based languages use the “main()” function as the start of the program – For example, set count to 100 when the program starts:

Implementing an Equation in App Inventor Area of a Rectangle = Length * Width – Step 1: What variables do we need? Area, Length, and Width – Step 2: Declare them in App Inventor – Step 3: Use Math. Operators to Implement

Output: The Label Component Label – Components used to show text. – Displays text specified by the Text property. – Useful Properties Text Width Visible Background Color

Output: The Image Component Image – Components used to show a picture – Displays text specified by the Picture property. – Useful Properties Picture Width Visible Height

Output: The Texting Component Texting – A non-visible component to allow users to send and receive text messages. – Useful Properties Message Phone Number Receiving Enabled (Does this also make the Texting component a input?)

Input: The Button Component Button – Components used to show text. – Displays text specified by the Text property. – Useful Properties Text Width Visible Background Color

Input: The TextBox Component TextBox – Components used to show text. – Displays text specified by the Text property. – Useful Properties Text Width Visible Background Color

Implementing the Algorithm: The Designer First, add the necessary components to in the Designer Window – 2 TextBoxes, a Button, and a Label – name your components AmountPaidBox TipPercentBox CalculateButton TipLabel – Remember, to put “Calculate Tip” on the button and remove the default label text

Next, need to declare and initialize our variables – Declare: amount_paid, tip_percentage, tip_amount – (Optional) Because it doesn’t make sense to have a 0% tip, let’s give it a default value of 5 and place that in the AmountTipBox at program startup

Next step: wait until the button is clicked Add a “When Button Clicked” Block to your code What’s the name of the button that needs to be clicked?

Next step: want us to get information from the textboxes What component variables (properties) represent the textbox data? What variables do we save this data to?

Next step: calculate the tip amount What variable represents the tip amount? Why do we divide tip percentage by 100???

Next step: display the tip amount to the user What component variables (properties) represent the label output?

Download to the Emulator and Test!!!

If-Blocks

Nesting If and If-Else Blocks Often times, we want to check if a prior condition is true, before checking another condition. – Example: If x > 100, then check if y is < 100. If y < 100, then assign z to 1. If x <= 100, set z to 35.

Implementation Step 1: Lamp Doesn’t Work – If-Block or If-Else Block? Why?

Step 2: Lamp Plugged In?

Step 3: Bulb Burned Out?