Language Basics

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

It is made of… Common elements in programming languages: Key Words Programmer-Defined Identifiers Operators Punctuation Syntax

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++.

Scratch https://scratch.mit.edu (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”.

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

Time for a Demo in class Will demo in class 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.

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

We will compare the following ideas in Scratch and a real C++ program Variables Keywords Operators Punctuation Syntax

This is our Program we will use Lets try it together on next slides This is our Program we will use You don’t know C++ But, try to read this C++ code. Read one line at a time --can you guess what it is doing just from reading it like English The comments can help DON’T WORRY – it will take us a few weeks to learn this –so relax

Variables

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.

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

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

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

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;

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.

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) The common name for hours, rate and pay in programming languages is VARIABLES

Keywords

Key Words Keywords tell us the definition of “things” in our program – we will learn what each of these do in the next few weeks

Operators

Operators Used to perform operations on data Many types of operators: Arithmetic - ex: +,-,*,/ Assignment – ex: = Some operators in Program1-1: << >> = * These are just like what you saw when you wrote math equations on paper --but, some like << and >> are new to programming –we will Learn them as we go

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

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

Punctuation

Punctuation Characters that mark the end of a statement, or that separate items in a list UNDERSTANDING Many but not ALL programming languages use the semi-colon ; to Indicate the end of a line of code. However, there are some languages like Python that just require each line of code to be on a separate line and don’t use semi-colons.

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

Punctuation in C++ WHY? Is it important to separate lines of code (in C++ with the semi-colon) --because the CPU/computer brain needs to process only one line at a time Commas = separate Semi-colons = end of line

Syntax

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)

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.

Program 1-1: lets look at it again comment too hard to guess –ignore for now Start of our program –the main “routine” These are variables –where we store values comment Asking user for hours-reading in value comment Asking user pay rate-reading in value DON’T WORRY – it will take us a few weeks to learn this –so relax comment Calculating the pay comment Print out to the user the pay

More about programming 

Input, Processing, and Output 1.5 Input, Processing, and Output

Input, Processing, and Output Three steps that a program typically performs: Gather input data: from keyboard (user types in) from files Process the input data Display the results as output: send it to the screen write to a file

The Programming Process 1.6 The Programming Process

The Programming Process

1.7 Procedural and Object-Oriented Programming ---- have you ever heard anyone say object oriented programming? How about procedural programming?

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 This class as your beginning C++ class focuses on Procedural Programming Scratch TIP: Our Sprites we saw in Scratch are like objects