Question

Code in c++ please fix all errors that’s being asked to find and please follow instructions

-------------------------------------------------

// This is example code from Chapter 6.7 "Trying the second version" of

// "Software - Principles and Practice using C++" by Bjarne Stroustrup

//

/*

This file is known as calculator02buggy.cpp

I have inserted 5 errors that should cause this not to compile

I have inserted 3 logic errors that should cause the program to give wrong results

First try to find an remove the bugs without looking in the book.

If that gets tedious, compare the code to that in the book.

Happy hunting!

*/

#include "std_lib_facilities.h"

//------------------------------------------------------------------------------

lass Token {

public:

char kind; // what kind of token

double value; // for numbers: a value

Token(char ch) // make a Token from a char

:kind(ch), value(0) { }

Token(char ch, double val) // make a Token from a char and a double

:kind(ch), value(val) { }

};

//------------------------------------------------------------------------------

class Token_stream {

public:

Token_stream(); // make a Token_stream that reads from cin

Token get(); // get a Token (get() is defined elsewhere)

void putback(Token t); // put a Token back

private:

bool full; // is there a Token in the buffer?

Token buffer; // here is where we keep a Token put back using putback()

};

//------------------------------------------------------------------------------

// The constructor just sets full to indicate that the buffer is empty:

Token_stream::Token_stream()

:full(false), buffer(0) // no Token in buffer

{

}

//------------------------------------------------------------------------------

// The putback() member function puts its argument back into the Token_stream's buffer:

void Token_stream::putback(Token t)

{

if (full) error("putback() into a full buffer");

buffer = t; // copy t to buffer

full = true; // buffer is now full

}

//------------------------------------------------------------------------------

Token get()

{

if (full) { // do we already have a Token ready?

// remove token from buffer

full=false;

return buffer;

}

char ch;

cin >> ch; // note that >> skips whitespace (space, newline, tab, etc.)

switch (ch) {

case ';': // for "print"

case 'q': // for "quit"

case '(': case ')': case '+': case '-': case '*': case '/':

return Token(ch); // let each character represent itself

case '.':

case '0': case '1': case '2': case '3': case '4':

case '5': case '6': case '7': case '9':

{

cin.putback(ch); // put digit back into the input stream

double val;

cin >> val; // read a floating-point number

return Token('8',val); // let '8' represent "a number"

}

default:

error("Bad token");

}

}

//------------------------------------------------------------------------------

Token_stream ts; // provides get() and putback()

//------------------------------------------------------------------------------

double expression(); // declaration so that primary() can call expression()

//------------------------------------------------------------------------------

// deal with numbers and parentheses

double primary()

{

Token t = ts.get();

switch (t.kind) {

case '(': // handle '(' expression ')'

{

double d = expression();

t = ts.get();

if (t.kind != ')') error("')' expected);

return d;

}

case '8': // we use '8' to represent a number

return t.value; // return the number's value

default:

error("primary expected");

}

}

//------------------------------------------------------------------------------

// deal with *, /, and %

double term()

{

double left = primary();

Token t = ts.get(); // get the next token from token stream

while(true) {

switch (t.kind) {

case '*':

left *= primary();

t = ts.get();

case '/':

{

double d = primary();

if (d == 0) error("divide by zero");

left /= d;

t = ts.get();

break;

}

default:

ts.putback(t); // put t back into the token stream

return left;

}

}

}

Answer 1

Below is the wrong code followed by the fixed code:

Q contains the wrong code and A contains the correct code where the correction is marked in bold.

===========================================================

Q:

lass Token {
public:
char kind; // what kind of token
double value; // for numbers: a value
Token(char ch) // make a Token from a char
:kind(ch), value(0) { }
Token(char ch, double val) // make a Token from a char and a double
:kind(ch), value(val) { }
};

A: class typo error:

class Token {
public:
    char kind;        // what kind of token
    double value;     // for numbers: a value
    Token(char ch)    // make a Token from a char
        :kind(ch), value(0) { }  
    Token(char ch, double val)     // make a Token from a char and a double
        :kind(ch), value(val) { }
};

===============================================================

Q:

class Token_stream {
public:
Token_stream(); // make a Token_stream that reads from cin
Token get(); // get a Token (get() is defined elsewhere)
void putback(Token t); // put a Token back
private:
bool full; // is there a Token in the buffer?
Token buffer; // here is where we keep a Token put back using putback()
};

A:

class Token_stream {
public:
Token_stream(); // make a Token_stream that reads from cin
Token get(); // get a Token (get() is defined in the below code segment)
void putback(Token t); // put a Token back
private:
bool full; // is there a Token in the buffer?
Token buffer; // here is where we keep a Token put back using putback()
};

============================================================

Q:

Token get()
{
if (full) { // do we already have a Token ready?
// remove token from buffer
full=false;
return buffer;
}

char ch;
cin >> ch; // note that >> skips whitespace (space, newline, tab, etc.)

switch (ch) {
case ';': // for "print"
case 'q': // for "quit"

case '(': case ')': case '+': case '-': case '*': case '/':
return Token(ch); // let each character represent itself
case '.':
case '0': case '1': case '2': case '3': case '4':
case '5': case '6': case '7': case '9':
{
cin.putback(ch); // put digit back into the input stream
double val;
cin >> val; // read a floating-point number
return Token('8',val); // let '8' represent "a number"
}
default:
error("Bad token");
}
}

A: Fixing the function type:

Token Token_stream::get(){
    if (full) {       // do we already have a Token ready?
        // remove token from buffer
        full=false;
        return buffer;
    }

    char ch;
    cin >> ch;    // note that >> skips whitespace (space, newline, tab, etc.)

    switch (ch) {
    case '=':    // for "print"
    case 'x':    // for "quit"
    case 'X':    // for "quit"
    case '(': case ')': case '+': case '-': case '*': case '/': case '%':
        return Token(ch);        // let each character represent itself
    case '.':
    case '0': case '1': case '2': case '3': case '4':
    case '5': case '6': case '7': case '8': case '9':
        {  
            cin.putback(ch);         // put digit back into the input stream
            double val;
            cin >> val;              // read a floating-point number
            return Token('8',val);   // let '8' represent "a number"
        }
    default:
        error("Bad token");
    }
}

==================================================================

Q:

double primary()
{
Token t = ts.get();
switch (t.kind) {
case '(': // handle '(' expression ')'
{
double d = expression();
t = ts.get();
if (t.kind != ')') error("')' expected);
return d;
}
case '8': // we use '8' to represent a number
return t.value; // return the number's value
default:
error("primary expected");
}
}

A: Closing braces error:

double primary()
{
    Token t = ts.get();
    switch (t.kind) {
    case '(':    // handle '(' expression ')'
        {  
            double d = expression();
            t = ts.get();
            if (t.kind != ')') error("')' expected"); //<- Fixed the closing braces.
            return d;
        }
    case '8':            // we use '8' to represent a number
        return t.value; // return the number's value
    default:
        error("primary expected");
    }
}

===================================================================

Q:

double term()
{
double left = primary();
Token t = ts.get(); // get the next token from token stream

while(true) {
switch (t.kind) {
case '*':

left *= primary();
t = ts.get();
case '/':
{
double d = primary();
if (d == 0) error("divide by zero");
left /= d;

t = ts.get();
break;
}
default:
ts.putback(t); // put t back into the token stream
return left;
}
}
}

A: Added missing braces and logic for the missing cases.

double term()
{
    double left = primary();
    Token t = ts.get();        // get the next token from token stream

    while(true) {
        switch (t.kind) {
        case '*':
            {
            left *= primary();
            t = ts.get();
            break;
            }
        case '/':
            {  
                double d = primary();
                if (d == 0) error("divide by zero");
                left /= d;
                t = ts.get();
                break;
            }
        case '%':
            {
                int d = primary();
                int l = left;
                if (d == 0) error("divide by zero");
                left = l%d;
                t = ts.get();
                break;
            }
        default:
            ts.putback(t);     // put t back into the token stream
            return left;
        }
    }
}