Comp 1672
Homework 5
Due Tuesday, Feb 11, 2003

1.  a.  False - this would destroy the usefulness of a class!
    b.  False - classes may have utility functions that are for internal use
    c.  True - it's recommended under most circumstances
    d.  False - see page 565
    e.  False - a constructor may, but a destructor never may
 
2.  a.  The second constructor returns an int - constructors never return values
    b.  It's better form to explicitly declare the data members as private
        The print function should be declared as void
        The semi-colon is missing at the end of the class declaration
    c.  It says "public;" and it should say "public:"
        The second constructor returns a bool - constructors never return values
         

Problem 3: 

#include <iostream>
#include <vector>
using namespace std;

class Two_by_two {
public:
    Two_by_two();
    Two_by_two(float, float, float, float);
    void set();
    void print_out();
    float det();
private:
    vector <float> data;
};

// default constructor - fill it with all 0s
Two_by_two::Two_by_two()
{
    for (int i=0; i < 4; i++)
        data.push_back(0);
}

// constructor - allows initialization of 4 values
Two_by_two::Two_by_two(float a, float b, float c, float d)
{
        data.push_back(a);
        data.push_back(b);
        data.push_back(c);
        data.push_back(d);
}

// input the 4 values from user
void Two_by_two::set()
{
    float a,b,c,d;
    data.clear();    // get rid of old values
    do {
        cout << "Please enter the 4 numbers: ";
        cin >> a >> b >> c >> d;
    } while (!cin);
    data.push_back(a);
    data.push_back(b);
    data.push_back(c);
    data.push_back(d);
}

// print out all four elements
void Two_by_two::print_out()
{
    vector <float>::iterator iter=data.begin();

    // output in two rows of two
    cout << *iter++ << " " << *iter++ << endl;
    cout << *iter++ << " " << *iter++ << endl;
}

float Two_by_two::det()
{
    return (data[0]*data[3] - data[1]*data[2]);
}

int main()
{
    Two_by_two matrix1;
    Two_by_two matrix2(1, 5, 2, 4);
    Two_by_two matrix3;

    cout << "Matrix 1: " << endl;
    matrix1.print_out();
    cout << "determinant: " << matrix1.det() << endl;
    cout << "Matrix 2: " << endl;
    matrix2.print_out();
    cout << "determinant: " << matrix2.det() << endl;
    cout << "Setting values in Matrix 3: " << endl;
    matrix3.set();
    matrix3.print_out();
    cout << "determinant: " << matrix3.det() << endl;
}