intro to programming with raptor

8/9/2019 Intro to Programming With RAPTOR

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D. Introduction to Programming with RAPTOR

By Lt Col Tom Schorsch

The RAPTOR Programming Language

RAPTOR is a visual programming language based on flowcharts. Flowcharts were developed asa design aid for developing programs; however, with RAPTOR they are a programming language

in their own right as the flowcharts you develop can be eecuted by the RAPTOR development

environment.

!e use RAPTOR in "#$$% for several reasons. First, the RAPTOR language has minimal

synta &grammar' when compared with other programming languages. This ma(es Raptor

programs easy to write as there are fewer language elements that you have to learn to beproductive. #econd the RAPTOR language is visual; RAPTOR programs are diagrams &directed

graphs'. One of the hardest aspects of programming to understand and get right is the flow of

control of the statements in your program. The visual nature of the flow of control in RAPTOR

programs ma(es them easier to understand and program. Third, we developed the programminglanguage and development environment. !e sought to ma(e the development environment easy

to use and the error messages that RAPTOR displays to you easy to understand. !e areconstantly trying to improve RAPTOR, so if you have suggestions please tell us. Fourth, our

purpose is not to teach you how to program in particular language. !e want to teach you how to

design and eecute algorithms to solve problems, and to implement algorithms using computer)based problem solving tools. These ob*ectives do not re+uire a heavy)weight commercial

programming language such as " or -ava.

!hat will you be missing by using RAPTOR instead of some other more conventionalprogramming language First, you will miss using a comple development environment that has

been designed to be useful to professional software developers but is etremely difficult to use inan educational environment by novice programmers. #econd, you will miss programming in alarge comple programming language with comple synta and semantics. Third, you will not

see cryptic error messages describing the multitude of synta errors you might commit while

programming in the comple programming language using the comple programmingenvironment.

RAPTOR Program Structure

A RAPTOR program is a directed graph. !hen eecuting a program, you begin at

the Startsymbol at the top and follow the arrows to eecute the program. Raptor

programs end with the Endsymbol. The smallest RAPTOR program &which does

nothing' is depicted at the right. /y placing additional RAPTOR statementsbetween the Start and End symbols you create more meaningful RAPTOR

programs.

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RAPTOR Variables

1ariables are memory locations that hold a value. At any given time a variable can only hold asingle value of a particular type of data, however, as the program eecutes, the data value stored

in the variable can change. They are called variables because the data stored by them can vary as

the program eecutes.

As an eample, the RAPTOR statement X32assigns the data value 32 to

the variable X. 2f that statement is followed by the statement XX+1 the

value of 32is retrieved from X, the value 1is added to it, and the result &33'

is stored bac( in variable X replacing the value that was previously stored

there. Thus, in the program at the right, the variable 3 initially had no value,

then it is assigned the value 32, then it is assigned the value 33, and finally it

is assigned the value 66. 2f you are reading this on)line &and have RAPTOR

installed' you can eecute the program by double)clic(ing here4 Variablevalue changing over time Examplerap. 5ou can step through the program

and see the value of variable 3 change by clic(ing on the button.

A variable is normally used to hold a value that is not (nown before the

program starts running. This value could be read in from the user, or itcould be computed from other values, and so the eact value that is

stored in the variable may vary every time the program is run &another

reason why it is called a variable'.

1ariables are one of the most important programming concepts as all

code involves the processing of data that is stored in variables. 2t isvariables, and their changing data values, that enable the same programs

to act differently every time you run them and to solve different versionsof the same problem. The program at the left gets a value from the user,the variable Numbercould have a different value each time the program

is eecuted. Variable value !i""erent each time the program is run

examplerap

An instructor will often as( a student to tell them the value of a variable. !hat they are as(ingfor is the value that was last assigned to that variable or was read into that variable at a

particular time during the programs execution. The first assignment of a value to a variable is

called initializing a variable. 1ariables do not automatically have values. 2f you try to use avariable6s value before it has been given one, epect a run)time error li(e the following.

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RAPTOR Statements

RAPTOR has > basic statements4 2nput, Output, Assignment, "all,

#election, and Eoop. Dach of these statements is indicated by a differentsymbol in RAPTOR as shown at the right.

The #election and Eoop statements are also called control structurestatements. They are control statements because they control how theprogram eecutes. They are structured statements because they can

enclose other statements.

The RAPTOR program

on the left contains

eamples of some of the> basic statements. The

comment eplains what

the program does. oticehow the loop statement

controls the eecution

flow and encloses otherstatements. Those of you

that have read 0ouglas

Adam6s boo(, The

Hitchhiker's Guide to the

Galaxy will understandthe reference.

2f you are reading this on)line you can eecute the program by clic(ing on4 The #ltimate$uestion o" Li"e% the #niverse an! Everythingrap,

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The RAPTOR program to the right

contains eamples of the remainingbasic statements.

The comment eplains what theprogram does. otice how the

selection control statement encloses

other statements and that only one ofthe statements will be eecuted. To

try it yourself, clic( here4

&ra'(Examplerap.

Statement

or

Instructio

n

A programming language instruction to the computer. An eecutable

statement that causes a specific action to occur when the program is run.

The Assignment, "all, 2nput, and Output statements are described below. A separate reading

describes the #election and Eoop control structure statements.

Assignment Statement

Programming often involves using formulas to compute

some value. The assignment statement is used to perform

a computation and then store the results in a variable. The

value stored in the variable can then be retrieved and usedin a later statement in the program.

The dialog bo at the right is used to enter both the name

of the variable being assigned and the computation that

will be evaluated and whose result will be assigned to thevariable.

Syntax "or an assignment statement1ariableG DpressionG or Set 1ariableG to DpressionG

An eample assignment statement is4

Cost (Tax_Rate Non_!ood_Tota"# + !ood_Tota"

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Assignment #ymbolDpression to be evaluated

and assigned during run time


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Expression

Any se+uence of literals, variables, operators, etc. that, during run)time, can

be evaluatedto produce a single value. That value is referred to as the resultof the expression.

The semantics for an assignment statement are4 Dvaluate the epression on the right hand side of the assignment operator.

Ta(e the value that was calculated and place it in the memory location associated with the

variable, replacing whatever data value had been stored there previously.

Assignmen

t

An assignment statement is used to modify or replace the data stored at thememory location associated with a variable.

Built in Operators and Functions

An operator or function directs the computer to perform some computation on data. Operatorsare placed between the data being operated on &i.e. X$3, %+&, etc.' whereas functions use

parentheses to indicate the data they are operating on &i.e. s'rt(), s*n(2)#'. !hen

eecuted, operators and functions perform their computation and return their result. RAPTOR

has the following built)in operators and functions.basic math4 +, ,, , $, -, , rem, mod, s'rt, "og, abs, .e*"*ng, /"oor

trigonometry4 s*n, .os, tan, .ot, ar.s*n, ar.os, ar.tan, ar..ot

relational4 0, 0, HI, , , 0, 0

logical4 and, or, not

miscellaneous4 random, 4engt5_o/

The basic math operators and functions include the familiar &+, ,, , $' as well as some that areunfamiliar.

and -are eponentiation, e 2is 16 3-2is

rem&remainder' and mod&modulus' return the remainder &what is left over' when the

right operand divides the left operand, e 17 rem 3is 1, 17 mod 3is 1also

s'rtreturns the s+uare root, e s'rt(#is 2

"ogreturns the natural logarithm, e "og(e#is 1

absreturns the absolute value, e abs(,#is

.e*"*ngrounds up to a whole number, e .e*"*ng(3)118#is

/"oorrounds down to a whole number, e /"oor(17$3#is 3

+also wor(s as a concatenation operation to *oin two strings or a string and a number,e 9T5e average *s : + (Tota" $ Number#

4engt5_;/returns the number of characters in a string variable &also the number of

elements in an array which you will learn about later', e Name 9Stu//:

followed by 4engt5_;/(Name#is 8

5ou should be familiar with the trigonometric functions &s*n, .os, tan, .ot, ar.s*n,

ar.os, ar.tan, ar..ot'. They wor( on angles whose units are radians. &i.e. you must

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1ariable being assigned


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The logical operators are defined by the following tables. The operands used by the logical

operators should be :/oolean< values &meaning the values returned by relational operators or

logical operators'.

Dpression ResultTrue andTrue TrueTrue and!a"se !a"se!a"se andTrue !a"se!a"se and!a"se !a"se

Dpression ResultTrue orTrue TrueTrue or!a"se True!a"se orTrue True!a"se or!a"se !a"se

Dpression Resultnot(True# !a"senot(!a"se# True

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The random function returns a number between % and $, e Xrandom could be %, %.7@,

%.>=?J, etc. 2f you need a random number in a different range then you can combine the

randomfunction with other operations. For eample, random177will evaluate to a number

between 7 and 177. .e*"*ng(random177#will evaluate to a whole number between 1

and 177.

Built in Constants

"onstants are pre)defined variables whose values cannot be changed. RAPTOR has the

following built)in constants.

constants4 =*, e, true, /a"se, 2>1&8176.

Trueand %esare defined to be 1.

!a"seand Noare defined to be 7.

The constants True, !a"se, %es, and Noare used by the RAPTOR eecution system to

determine the results of a decision.

Proce!ure Call statements

5ou have heard that a pilot follows ta(e)off and landing procedures, a car mechanic follows a

procedure to change your oil or replace your transmission, and you probably have a procedurefor shining your shoes. 2 follow the change)oil procedure myself, but 2 get a car mechanic to do

the replace transmission procedure for me when that becomes necessary. Typically, a procedure

has something that it is acting upon, li(e the specific transmission and car. #imilarly, a calledprocedure often must be supplied data, and it often returns data. 2n this class you will only be

calling procedures, not creating procedures.

A procedure is a named collection of programming statements that accomplish a tas(. "alling aprocedure suspends eecution of your program, eecutes the steps associated with the called

procedure, and then returns bac( and starts eecuting your program again. 5ou do not have to

see the instructions or even (now what they are in order to use a procedure; you *ust have to(now what the procedure will do to use it properly.

To use an eisting procedure, you must callit by invo(ing its name and providing it with data

that it needs. 5ou may call a procedure many times sending it different data each time.#imilarly, a car mechanic may (now the procedure for replacing a transmission &or it could be

written down in a boo(' and could eecute that procedure on many different cars and rebuilttransmissions. Thus you can tal( and reason about the procedure separately from the specific

item &be it a specific transmission or a specific piece of data' a procedure is acting upon.

The 0raw Dample &several pages ago' contained @ eamples of procedure calls which arerepeated below. The first opens up a graphics window that is $%% piels wide by $%% piels high.

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The second draws a circle centered at piel =%, =% with a radius of 7= piels. The last draws a

bo that has a lower left corner at piel 7=, 7= and an upper right corner at piel ?=, ?=. /oth the

circle and s+uare are blac( in color and both are filled. /y changing any of the data being passedinto the procedure, you change what the procedure does.

Built in Procedure

The de"a


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Output statements

2n RAPTOR, an output statement is a special type of procedure thatdisplays a value to the output screen. A dialog bo as(s you to identify whether you are writing

out an epression or tet &using a radio button' and whether a new line will be output &using a

chec(bo'. The dialog boes depict different eamples depending on whether umber or Tetoutput is chosen &see below'.

!hen outputting tet, you can place additional spaces after the tet as shown in the dialog bo to

the left above and in the RAPTOR program to the right above. This will cause the umberoutput to be separated from the tet by a space. !hen outputting an Dpression, you can write

out a mathematical epression as well as a variable as shown in the dialog bo in the middle

above.

5our instructor &or your assignment' will also often say :0isplay the results in a user)friendly

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Selection an! Loop statements

As mentioned previously, the selection and loop statements are described in a separate reading.

Comments in RAPTOR

RAPTOR, li(e many other programming languages, allows you to add comments to yourprogram. The sole purpose of a comment is to eplain some aspect of a program. "omments

should inform or add information for the reader, especially in places where the program code is

comple and hard to understand. "omments are not eecuted and mean nothing to the computerbut can be very informative to the human reader.

CommentDplanatory tet that is written for the human reader of the program code.

"omments are not instructions to the computer.

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*hat 'e have learne!+

!e understand the basic structure and parts of a RAPTOR program.

!e (now what the arithmetic, logical, and relational operators are and what they can do.

!e (now purposes of and how to use the > basic RAPTOR statements.

!e (now how to display information in a user)friendly fashion.

!e understand what an epression is and can evaluate an epression to determine its value.

!e can assign a value to a variable using an assignment statement

Rea!ing Sel",Chec-

$. Eabel the following RAPTOR identifiers as &L' legal or &)' 2llegal. 2f illegal then eplain why.KKKK $' T5*s_@s_A_Test

KKKK 7' _2

KKKK @' Bone


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KKKKKKKKKK ' 6 2

KKKKKKKKKK =' 12 13

KKKKKKKKKK >' 38 7

KKKKKKKKKK ?' 127 $0 672

KKKKKKKKKK J' 6 )8

KKKKKKKKKK B' True and!a"seKKKKKKKKKK $%' (!a"se and!a"se# orTrue

KKKKKKKKKK $$' &8)6 32)# or(1 2>#

KKKKKKKKKK $7' > 17 27

KKKKKKKKKK $@' True and&

KKKKKKKKKK $' 121)86

KKKKKKKKKK $=' && + ,112>

KKKKKKKKKK $>' &@ L @'LL7 J% or&True an!&>?.= $7$.=''

=. 2dentify the following as &A' Arithmetic, &E' Eogical, or &R' relational operators.

KKKK $' 0

KKKK 7'

KKKK @' $

KKKK ' not

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