Exercise Solutions

Top

int IStack::Top () const
{
    assert (_top > 0);
    return _arr [_top - 1];
}

int IStack::Count () const
{    return _top;
}

This example calls Pop on an empty stack, in violation of the contract.
int main () { IStack stack; stack.Pop (); }

This is the interface of the stack of characters:

class CharStack
{
public:
    CharStack () :_top (0) {}
    void Push (char c);
    char Pop ();
    char Top () const;
    int Count () const;
private:
    char _arr [maxStack];
    int  _top;
};

This is how you reverse a string using a stack of characters:

int main ()
{
    CharStack stack;
    char str [] = "esreveR";
    for (int i = 0; str [i] != '\0'; ++i)
        stack.Push (str [i]);
    while (stack.Count () > 0)
        std::cout << stack.Pop ();
    std::cout << std::endl;
}

Queue

#include 
#include 

const int maxPuts = 8;

class Queue
{
public:
    Queue ();
    double Get ();
    void Put (double x);
private:
    double    _arr [maxPuts];
    int        _putIdx;
    int        _getIdx;
};

Queue::Queue ()
: _putIdx (0),
_getIdx (0)
{}

double Queue::Get ()
{
    assert (_getIdx < _putIdx);
    ++_getIdx;
    return _arr [_getIdx - 1];
}

void Queue::Put (double x)
{
    assert (_putIdx < maxPuts);
    _arr [_putIdx] = x;
|    ++_putIdx;
}
|
int main ()
{
    Queue queue;
    queue.Put (0.1);
    queue.Put (0.2);
    std::cout << "Getting: " << queue.Get () << ", " 
        << queue.Get () << std::endl;
    queue.Put (0.3);
    std::cout << "Getting more: " << queue.Get () << std::endl; 
}

Array of double

#include 
#include 

const int maxCells = 16;

class DblArray
{
public:
    DblArray ();
    void Set (int i, double val);
    double Get (int i) const;
    bool IsSet (int i) const;
private:
    double    _arr [maxCells];
    bool    _isSet [maxCells];
};

DblArray::DblArray ()
{
    for (int i = 0; i < maxCells; ++i)
        _isSet [i] = false;
}

void DblArray::Set (int i, double val)
{
    assert (i < maxCells);
    assert (!IsSet (i));
    _arr [i] = val;
    _isSet [i] = true;
}

double DblArray::Get (int i) const
{
    assert (i < maxCells);
    assert (_isSet [i]);
    return _arr [i];
}

bool DblArray::IsSet (int i) const
{
    assert (i < maxCells);
    return _isSet [i];
}

int main ()
{
    DblArray arr;
    arr.Set (2, 0.2);
    arr.Set (4, 0.4);
    std::cout << "IsSet (0) returns " << arr.IsSet (0) << std::endl;
    std::cout << "IsSet (2) returns " << arr.IsSet (2) << std::endl;
    std::cout << "Get (2) returns " << arr.Get (2) << std::endl;
    std::cout << "Get (4) returns " << arr.Get (4) << std::endl;
}