Variables

What will we learn today? What Are Variables Variables in Real-Life Variables in Programs Types of Variables Creating a Timer Example

Variables A Variable is a storage location (place in computer’s memory) which contains information Variables are analogous to "Buckets" or "Envelopes" where information can be maintained and referenced Each variable has a name (an identifier), a type and a value (piece of information) E.g. (a=5, b=“hello”) Variables allow us to keep track of changes as our program runs

Variables in Real Life We use variables to track the balance of money in a bank account We use variables to track the amount of gasoline in the tank of the car

Variables in Programs We often need to keep track of changes in position, color, and other properties of objects in our programs In a game, we may want to keep track of number of steps or times or numbers of goals..etc For example, we want to know the number of times a player has put the basketball through the hoop or how much time is left on the clock

Types of Variables Numeric Boolean Character/String Object They can store a whole number value, e.g. 7 or 1024 Boolean They can represent one of two states, true or false Character/String They can represent a single character, e.g. 'A' or '$‘ or a group of characters, e.g. “Ali” or “20 minutes left” Object They can represent a whole object, e.g. cat or fort

A Timer for a Game Example A timer is used in most of the games to keep track of how much time the player has left to play We will construct a timer that counts down in seconds Our task is to set the timer to an initial number of seconds (e.g. 10s) and then count down the seconds remaining in a game The number of seconds remaining will be displayed and will be updated with each passing second We will create a chicken that rotates around itself as the timer count down

A Timer for a Game Example Add a new object: a 3D text Type 0.0 which is the value that appears when the time’s over

A Timer for a Game Example Rename the object to timer

A Timer for a Game Example Add a new variable in the timer object Select the timer object Select the properties tab Click on the ‘create new variable’ button Name it ‘timeLeft’ and set it to type ‘number’

A Timer for a Game Example Drag the ‘timeLeft’ to the ‘world.timer’ method Create a new parameter and call it ‘amount of time’

A Timer for a Game Example Set the values as shown Create a new method and call it ‘countDown’

A Timer for a Game Example Inside the method, add a while loop with expression ‘a<b’ and set ‘a’ and ‘b’ as follows Drag the text inside the while loop

A Timer for a Game Example Set the value of the text as follows, drag ‘what’ from the functions box Drag time left from properties insert it into the what box

A Timer for a Game Example Move the timer up and down Make a function that returns the time left

A Timer for a Game Example The ‘countDown’ method Create a method ‘playGame’ and set it as follows

A Timer for a Game Example The main method ‘world.myFirst’ method

A Timer for a Game Example Here is our Chicken

Let’s Work with Alice Counting Fishes A Scuba diver (people) wants to count the fishes (ocean) that eat from the Seaweed (ocean). Make a method where each fish goes to the seaweed, eats, waits, and comes back. As each fish does so, a counter on the top-right corner of the screen (3D-Text) increases by one. After all fish have eaten, the scuba diver says the final count of fishes. You will need to create a number variable ‘NumberOfFish’ for that.