Turtle Graphics代写、代做C/C++语言、代写Adding Loops、代做C++程序

日期：2019-01-14 10:22

12. Final Assignment : Parsing

12.1 Turtle Graphics

History

Many attempts have been made to create programming languages which are intuitive and

easy to learn.

One of the best of these was LOGO which allowed children as young as 3 to learn a

computer language.

A subset of this language involved a “turtle” which could be driven around the screen

using simple instructions. The turtle, when viewed from above, was represented by a

triangle.

An Example

{

FD 30

LT 45

FD 30

LT 45

FD 30

LT 45

FD 30

LT 45

FD 30

LT 45

FD 30

LT 45

FD 30

LT 45

FD 30

LT 45

}

2 Chapter 12. Final Assignment : Parsing

Adding Loops

{

DO A FROM 1 TO 8 {

FD 30

LT 45

}

}

Using Variables

{

DO A FROM 1 TO 100 {

SET C := A 1.5 * ;

FD C

RT 62

}

}

12.1 Turtle Graphics 3

Nested Loops

{

DO A FROM 1 TO 50 {

FD A

RT 30

DO B FROM 1 TO 8 {

SET C := A 5 / ;

FD C

RT 45

}

}

}

4 Chapter 12. Final Assignment : Parsing

The Formal Grammar

<MAIN> ::= "{" <INSTRCTLST>

<INSTRCTLST> ::= <INSTRUCTION><INSTRCTLST> |

"}"

<INSTRUCTION> ::= <FD> |

<LT> |

<RT> |

<DO> |

<SET>

<FD> ::= "FD" <VARNUM>

<LT> ::= "LT" <VARNUM>

<RT> ::= "RT" <VARNUM>

<DO> ::= "DO" <VAR> "FROM" <VARNUM> "TO"

<VARNUM> "{" <INSTRCTLST>

<VAR> ::= [A?Z]

<VARNUM> ::= number | <VAR>

<SET> ::= "SET" <VAR> ":=" <POLISH>

<POLISH> ::= <OP> <POLISH> | <VARNUM> <POLISH> | ";"

<OP> ::= "+" | "?" | "*" | "/"

12.2 Assessment 5

12.2 Assessment

Exercise 12.1 Implement a recursive descent parser - this will report whether or not a given

turtle program follows the formal grammar or not. The input file is specified via argv[1] -

there is no output if the input file is valid. Elsewise, a non-zero exit is made. 

Exercise 12.2 Extend the parser, so it becomes an interpreter. The instructions are now

‘executed’. Do not write a new program for this, simply extend your existing parser. Output

is via SDL. You may find the function call SDL_RenderDrawLine useful. 

Exercise 12.3 Show a testing strategy on the above - you should give details of unit testing,

white/black-box testing done on your code. Describe any test-harnesses used. In addition,

give examples of the output of many different turtle programs. Convince me that every line

of your C code has been tested. 

Exercise 12.4 Show an extension to the project in a direction of your choice. It should

demonstrate your understanding of some aspect of programming or S/W engineering. If

you extend the formal grammar make sure that you show the new, full grammar. 

Hints

All four sections above are equally weighted.

Don’t try to write the entire program in one go. Try a cut down version of the grammar

first, e.g.:

<MAIN> ::= "{" <INSTRCTLST>

<INSTRCTLST> ::= <INSTRUCTION><INSTRCTLST> |

"}"

<INSTRUCTION> ::= <FD> | <LT> | <RT>

<FD> ::= "FD" <VARNUM>

<LT> ::= "LT" <VARNUM>

<RT> ::= "RT" <VARNUM>

<VARNUM> ::= number

The language is simply a sequence of words (even the semi-colons), so use fscanf().

Some issues, such as what happens if you use an undefined variable, or if you use a variable

before it is set, are not explained by the formal grammar. Use your own common-sense,

and explain what you have done.

Once your parser works, extend it to become an interpreter. DO NOT aim to parse the

program first and then interpret it separately. Interpreting and parsing are inseparably

bound together.

I’m happy to sort extra help sessions in January - ask.

Submission

Your testing strategy will be explained in testing.txt, and your extension as extension.txt.

For the parser, interpreter and extension sections, make sure there’s a Makefile, so that I can

easily build the code using make parse, make interp and make extension.