1. Language Basics

2. What is a Program Made of?
Chapter 1.4
What is a Program Made of?

3. Last lecture I said… Common elements in programming languages:
Key Words
Programmer-Defined Identifiers
Operators
Punctuation
Syntax

4. Wow!!! I am overwhelmed ---what does all of this mean.
Don’t worry---lets play a bit and learn a little bit about these idea with a fun tool called Scratch before we learn about C++.

5. Scratch (scratch.mit.edu)
Application to teach concepts of Programming that is language independent and geared for children
What is it really = a visual editor where you don’t have to worry about language syntax and you can create games/animations that others can “play”.

6. Scratch Preview Panel- can view current game/animation here
Scripting Panel- THIS IS WHERE WE CREATE OUR CODE
Toolkit Panel- where can get the operators of the Scratch LANGUAGE
Sprite Panel—where
you make your characters in
your game

7. Time for a Demo in class
Uses beginning project linked on our class website or see instructor.
NOTE how the language statements SNAP together like Legos --- this is like writing good
Syntax in a program – only certain statements can go with others in a language.

8. Lets compare concepts of real programs with Scratch to really Learn what these ideas mean

9. We will compare the following ideas in Scratch and a real C++ program
Programmer-Defined Identifiers --- variables
Operators
Punctuation
Syntax

10. This is our Program we will use

11. Programmer-Defined Identifiers --Variables
Names made up by the programmer
Not part of the programming language
Used to represent various things: variables (memory locations), functions, etc.

12. Variables in Scratch
Scratch we have character’s named Sprites --- we can define variables about them.

13. Variables in a Program
A variable is a named storage location in the computer’s memory for holding a piece of data.

14. Variables in C++ example
In Program 1-1 we used three variables:
The hours variable was used to hold the hours worked
The rate variable was used to hold the pay rate
The pay variable was used to hold the gross pay

15. Variable Definitions
To create a variable in a program you must write a variable definition (also called a variable declaration)
Here is the statement from Program 1-1 that defines the variables: double hours, rate, pay;

16. Variable Definitions
There are many different types of data, which you will learn about in this course.
A variable holds a specific type of data.
The variable definition specifies the type of data a variable can hold, and the variable name.

17. Variable Definitions
Once again, line 7 from Program 1-1: double hours, rate, pay;
The word double specifies that the variables can hold double-precision floating point numbers. (You will learn more about that in Chapter 2)

18. Operators Used to perform operations on data Many types of operators:
Arithmetic - ex: +,-,*,/
Assignment – ex: =

19. Operators in Scratch Lets look at addition in Scratch
When Cat moves lets change location by +10 each time.

20. Operators in C++ example (<< >> = * )

21. Punctuation
Characters that mark the end of a statement, or that separate items in a list

22. Scratch – no punctuation –but end of line is visible
Here each line of code has its own “shaped box”

23. Punctuation in C++
Commas = separate
Semi-colons = end of line

24. Syntax
The rules of grammar that must be followed when writing a program
Controls the use of key words, operators, programmer-defined symbols, and punctuation
Scratch TIP: controls syntax remember by
Only allowing certain commands to “SNAP” together.
Here we see the “if” statement does something (turns 15 degrees) when the (distance to Sprite1 is < 20)

25. Example Syntax in C++
Regular statements must end with a Semi- colon ---this signifies the end of the statement
We will learn more of the
C++ sytnax rules as we go
through the class.

26. Procedural and Object-Oriented Programming
---- what did I mean in last lecture --- can Scratch help us?

27. Procedural and Object-Oriented Programming
Procedural programming: focus is on the process. Procedures/functions are written to process data.
Object-Oriented programming: focus is on objects, which contain data and the means to manipulate the data. Messages sent to objects to perform operations.
Scratch TIP: Our operations like when we are close to Sprite1 then turn 15 degrees is a procedure
Scratch TIP: Our Sprites we saw in Scratch are like objects