The second project involves completing and extending the C++ program that evalua
ID: 3675952 • Letter: T
Question
The second project involves completing and extending the C++ program that evaluates statements of an expression language contained in the module 3 case study. The statements of that expression language consist of an arithmetic expression followed by a list of assignments. Assignments are separated from the expression and each other by commas. A semicolon terminates the expression. The arithmetic expressions are fully parenthesized infix expressions containing integer literals and variables. The valid arithmetic operators are +, –, *, /. Tokens can be separated by any number of spaces. Variable names begin with an alphabetic character, followed by any number of alphanumeric characters. Variable names are case sensitive. This syntax is described by BNF and regular expressions in the case study.
The program reads in the arithmetic expression and encodes the expression as a binary tree. After the expression has been read in, the variable assignments are read in and the variables and their values of the variables are placed into the symbol table. Finally the expression is evaluated recursively.
Your first task is to complete the program provided by providing the three missing classes, Minus, Times and Divide.
Next, you should extend the program so that it supports relational, logical and conditional expression operators as defined by the following extension to the grammar:
Note that there are a few differences in the use of these operators compared to their customary use in the C family of languages. There differences are
In the conditional expression operator the symbols are reversed and the third operand represents the condition. The first operand is the value when true and the second the value when false
The logical operators use single symbols not double, for example the and operator is & not &&
The negation operator ! is a postfix operator, not a prefix one
There are only three relational operators not the usual six and the operator for equality is = not ==
Like C and C++, any arithmetic expression can be interpreted as a logical value, taking 0 as false and anything else as true
Your final task is to make the following two modifications to the program:
The program should accept input from a file, allowing for multiple expressions arranged one per line. Some hints for accomplishing this transformation will be provided in the conference
All results should be changed from double to int. In particular the evaluate function should return an int.
You may assume that all input to the program is syntactically correct.
You are to submit the source code for the entire program in a .zip file. Your program must compile with Microsoft Visual C++ or any modern C/C++ compiler on your O/S.
Explanation / Answer
minus.h:
//define the class Minus subclass of the SubExpression
class Minus : public SubExpression
{
public:
//define the default construtor
Minus(Expression* left, Expression* right) : SubExpression(left, right)
{
}
//define the function evaluate()
double evaluate()
{
//subtract the value of right from the value of the left
//and return the value.
return left->evaluate() - right->evaluate();
}
};
times.h:
//define the class Minus subclass of the SubExpression
class Times : public SubExpression
{
public:
//define the default construtor
Times(Expression* left, Expression* right) : SubExpression(left, right)
{
}
//define the function evaluate()
double evaluate()
{
//multiple the value of right and value of the left
//and return the value.
return left->evaluate() * right->evaluate();
}
};
divide.h:
//define the class Minus subclass of the SubExpression
class Divide : public SubExpression
{
public:
//define the default construtor
Divide(Expression* left, Expression* right) : SubExpression(left, right)
{
}
//define the function evaluate()
double evaluate()
{
//divide the value of left and value of the right
//and return the value.
return left->evaluate() / right->evaluate();
}
};
plus.h:
//define the class Plus subclass of the SubExpression
class Plus: public SubExpression
{
public:
//define the default construtor
Plus(Expression* left, Expression* right): SubExpression(left, right)
{
}
//define the function evaluate()
double evaluate()
{
//adds the value of left and value of the right
//and return the value.
return left->evaluate() + right->evaluate();
}
};
expression.h:
//define the class Expression
class Expression
{
public:
//declare a virtual function evaluate()
virtual double evaluate() = 0;
};
subexpression.h:
//define the class SubExpression subclass of the Expression
class SubExpression : public Expression
{
public:
//constructor
SubExpression(Expression* left, Expression* right);
//declare a static function parse()
static Expression* parse();
protected:
//declare the variables
Expression* left;
Expression* right;
};
operand.h:
//define the class Operand subclass of the Expression
class Operand : public Expression
{
public:
//declare a static function parse()
static Expression* parse();
};
variable.h:
#include <strstream>
#include <vector>
using namespace std;
//define the class Variable subclass of the Operand
class Variable : public Operand
{
public:
//define the construtor
Variable(string name)
{
this->name = name;
}
//define the function evaluate()
double Variable::evaluate();
private:
string name;
};
parse.h:
#include <iostream>
#include <string>
//declare a function parseName()
string parseName();
literal.h:
//define the class Literal subclass of the Operand
class Literal : public Operand
{
public:
//define the construtor
Literal(int value)
{
this->value = value;
}
//define the function evaluate()
//returns the value
double evaluate()
{
return value;
}
private:
int value;
};
symboltable.h:
//define the class SubExpression
class SymbolTable
{
public:
//constructor
SymbolTable() {}
//declare the function
void insert(string variable, double value);
double lookUp(string variable) const;
private:
//define the structure Symbol
struct Symbol
{
Symbol(string variable, double value)
{
this->variable = variable;
this->value = value;
}
string variable;
double value;
};
//create a vector of type Symbol
vector <Symbol> elements;
};
operand.cpp:
#include <cctype>
#include <iostream>
#include <list>
#include <string>
using namespace std;
#include "expression.h"
#include "subexpression.h"
#include "operand.h"
#include "variable.h"
#include "literal.h"
#include "parse.h"
//definition of the function parse()
Expression* Operand::parse()
{
char paren;
double value;
cin >> ws;
if (isdigit(cin.peek()))
{
cin >> value;
Expression* literal = new Literal(value);
return literal;
}
if (cin.peek() == '(')
{
cin >> paren;
return SubExpression::parse();
}
else
return new Variable(parseName());
return 0;
}
variable.cpp
#include <strstream>
#include <vector>
using namespace std;
#include "expression.h"
#include "operand.h"
#include "variable.h"
#include "symboltable.h"
//create an object of SymbolTable
extern SymbolTable symbolTable;
//definition of the function evaluate()
double Variable::evaluate()
{
//return the name from the symbolTable
return symbolTable.lookUp(name);
}
symboltable.cpp:
#include <string>
#include <vector>
using namespace std;
#include "symboltable.h"
//definition of the function insert()
void SymbolTable::insert(string variable, double value)
{
//push the symbol in to the vector
const Symbol& symbol = Symbol(variable, value);
elements.push_back(symbol);
}
//definition of the function lookUp()
double SymbolTable::lookUp(string variable) const
{
//search in the vector and return the value.
for (int i = 0; i < elements.size(); i++)
if (elements[i].variable == variable)
return elements[i].value;
return -1;
}
subexpression.cpp
#include <iostream>
using namespace std;
#include "expression.h"
#include "subexpression.h"
#include "operand.h"
#include "plus.h"
#include "minus.h"
#include "times.h"
#include "divide.h"
//define the constructor
SubExpression::SubExpression(Expression* left, Expression* right)
{
this->left = left;
this->right = right;
}
//definition of the class parse()
Expression* SubExpression::parse()
{
Expression* left;
Expression* right;
char operation, paren;
//read the Operand
left = Operand::parse();
//read the operation
cin >> operation;
//read the Operand
right = Operand::parse();
//read the paren
cin >> paren;
switch (operation)
{
case '+':
return new Plus(left, right);
case '-':
return new Minus(left, right);
case '*':
return new Times(left, right);
case '/':
return new Divide(left, right);
}
system("pause");
return 0;
}
parse.cpp
#include <cctype>
#include <iostream>
#include <string>
using namespace std;
#include "parse.h"
//definition of the function parseName()
string parseName()
{
char alnum;
string name = "";
cin >> ws;
while (isalnum(cin.peek()))
{
cin >> alnum;
name += alnum;
}
return name;
}
main.cpp:
#include <iostream>
#include <string>
#include <vector>
using namespace std;
#include "expression.h"
#include "subexpression.h"
#include "symboltable.h"
#include "parse.h"
//create an object of SymbolTable
SymbolTable symbolTable;
//prototype of the function
void parseAssignments();
//define main function
int main()
{
Expression* expression;
char paren, comma;
cout << "Enter expression: ";
cin >> paren;
expression = SubExpression::parse();
cin >> comma;
parseAssignments();
cout << "Value = " << expression->evaluate() << endl;
cin>>comma;
return 0;
}
//definition of the function parseAssignments()
void parseAssignments()
{
char assignop, delimiter;
string variable;
double value;
do
{
variable = parseName();
cin >> ws >> assignop >> value >> delimiter;
symbolTable.insert(variable, value);
}
while (delimiter == ',');
}