代做ECS 140A Fall 2024 Midterm 1 Review代做留学生C/C++语言

日期：2024-10-31 06:05

ECS 140A  Fall 2024

Midterm 1 Review

Derivation, Parse Tree, EBNF, Ambiguity, First Sets, Construct a Parser, Java, Semantics

In addition to the following topics, make sure you have studied all the lecture and discussion    slides (everything before functional programming in lecture 9), as well as the relevant textbook chapters.

Table of Contents:

BNF Grammar

Derivation

Parse tree

Ambiguity

Recursion and associativity

EBNF

First sets

Parser

Java

Binding

Scoping

BNF Grammar

This BNF grammar will be used in all of the subsequent review problems.

<arith_expr> ::= <arith_expr> + <arith_term> | <arith_expr> - <arith_term> | <arith_term> <arith_term> ::= <arith_term> * <arith_unit> | <arith_term> / <arith_unit> | <arith_unit>     <arith_unit> ::= num | -num | ( <arith_expr> )

Assume num is a terminal symbol and can be 0..9.

Derivation

Show the left-most derivation for 8 - 2 * ( 1 + (-4)). Assume your start symbol is <arith_expr>. Is the following derivation correct for 8 - 2 * ( 1 + (-4))?Incorrect.

<arith_expr> ::= <arith_expr> - <arith_term>

<arith_expr> ::= <arith_term> - <arith_term> - <arith_term>

<arith_expr> ::= <arith_unit> - <arith_term> - <arith_term>

<arith_expr> ::= num - <arith_term> - <arith_term>

<arith_expr> ::= num - <arith_term> - <arith_term> * <arith_unit>

<arith_expr> ::= num - <arith_term> - <arith_unit> * <arith_unit>

<arith_expr> ::= num - <arith_unit> - <arith_unit> * <arith_unit>

<arith_expr> ::= num - num - <arith_unit> * <arith_unit>

<arith_expr> ::= num - num - ( <arith_expr> ) * <arith_unit>

<arith_expr> ::= num - num - ( <arith_expr> + <arith_term> ) * <arith_unit>

<arith_expr> ::= num - num - ( <arith_term> + <arith_term> ) * <arith_unit>

<arith_expr> ::= num - num - ( <arith_unit> + <arith_term> ) * <arith_unit>

<arith_expr> ::= num - num - ( num + <arith_term> ) * <arith_unit>

<arith_expr> ::= num - num - ( num + <arith_unit> ) * <arith_unit>

<arith_expr> ::= num - num - ( num +  ( <arith_expr> ) ) * <arith_unit>

<arith_expr> ::= num - num - ( num +  ( <arith_term> ) ) * <arith_unit>

<arith_expr> ::= num - num - ( num +  ( <arith_unit> ) ) * <arith_unit> 

<arith_expr> ::= num - num - ( num + ( - num ) ) * <arith_unit>

<arith_expr> ::= num - num - ( num + ( - num ) ) * num

Parse tree

Show the parse tree for 8 - 2 * ( 1 + (-4))

Ambiguity

Is this grammar ambiguous? Why or why not?

Does + and - have higher or lower precedence than * and / in this grammar?

Recursion and associativity

Are there left recursions or right recursions in the grammar? Left associative or right associative?

EBNF

Convert the grammar to EBNF.

First sets

Compute the first sets for all non-terminal symbols based on EBNF.

Parser

Based on the EBNF grammar and first sets you created, construct a simple parser like the

example we went through in lecture and discussion. Assume you have access to next(), error(), f_X, and sym.

Java

Implement a basic StringManipulator class in Java with methods to reverse a string,

convert a string to uppercase, and check if a string is a palindrome. Make sure you use correct data types. Here is a sample test class that will be used to test your StringManipulator

class.

public class StringManipulatorTest {

public static void main(String [] args) {

StringManipulator manipulator = new StringManipulator (); //

create a new StringManipulator instance

String riginal = "level";

String reversed = manipulator.reverseString (original);

System.out.println ("Reversed string: " + reversed);

// Should print: Reversed string: level

String uppercase = manipulator.toUpperCase (original);

System.out.println ("Uppercase string: " + uppercase);

// Should print: Uppercase string: LEVEL

boolean isPalindrome = manipulator.isPalindrome (original);

System.out.println ("Is palindrome: " + isPalindrome);

// Should print: Is palindrome: true

}

}

Binding

Given the following simple assignment statement in C++:

`a = b + c;`

The statement contains the following components:

- Identifies: a, b, c

- Operators: =, +

For each component of the statement, list the various bindings that are required to

determine the semantics when the statement is executed. For each binding, indicate the binding time used for the language. Explain your answer.

Scoping

Consider the following program. If static scoping is in use, what is written?

begin

integer x;

procedure f;

begin

x = x + 3;

end

x = 20;

begin

integer x;

x = 10;

f;

write x;

end

f;

write x;

end

Consider the following program. If dynamic scoping is in use, what is written?

begin

integer x;

procedure f;

begin

x = x + 3;

end

x = 20;

begin

integer x;

x = 10;

f;

write x;

end

f;

write x;

end