Language Basics

Chapter 1.4Chapter 1.4What is a Program Made of?

Last lecture I said…Last lecture I said…Common elements in

programming languages:◦Key Words◦Programmer-Defined Identifiers◦Operators◦Punctuation◦Syntax

Wow!!!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++.

ScratchScratch

(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”.

ScratchScratch

Sprite Panel—whereyou make your characters inyour game

Preview Panel- can view currentgame/animation here

Scripting Panel- THIS IS WHERE WE CREATE OUR CODEToolkit

Panel- where can get the operators of the Scratch LANGUAGE

Time for a Demo in classTime for a Demo in classUses beginning project linked on our

class website or see instructor.

NOTE how the language statements SNAP together like Legos --- this is like writing goodSyntax in a program – only certain statements can go with others in a language.

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

We will compare the We will compare the following ideas in Scratch following ideas in Scratch and a real C++ programand a real C++ program

◦Programmer-Defined Identifiers --- variables

◦Operators◦Punctuation◦Syntax

This is our Program we will This is our Program we will useuse

Programmer-Defined Programmer-Defined Identifiers --VariablesIdentifiers --VariablesNames made up by the

programmerNot part of the programming

languageUsed to represent various things:

variables (memory locations), functions, etc.

Variables in ScratchVariables in Scratch

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

Variables in a ProgramVariables in a ProgramA variable is a named storage

location in the computer’s memory for holding a piece of data.

Variables in C++Variables in C++exampleexample

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 DefinitionsVariable DefinitionsTo 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 DefinitionsVariable DefinitionsThere 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 DefinitionsVariable DefinitionsOnce 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)

OperatorsOperatorsUsed to perform operations on

dataMany types of operators:

◦Arithmetic - ex: +,-,*,/◦Assignment – ex: =

Operators in ScratchOperators in Scratch

Lets look at addition in Scratch

When Cat moves lets change location by +10 each time.

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

PunctuationPunctuationCharacters that mark the end of

a statement, or that separate items in a list

Scratch – no punctuation –Scratch – no punctuation –but end of line is visiblebut end of line is visibleHere each

line of code hasits own “shapedbox”

Punctuation in C++Punctuation in C++Commas = separateSemi-colons = end of line

SyntaxSyntaxThe 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 byOnly 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++Example Syntax in C++Regular statements must end

with a Semi-colon ---this signifies the end of the statement

We will learn more of theC++ sytnax rules as we go through the class.

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

Procedural and Object-Procedural and Object-Oriented ProgrammingOriented 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