
Class demonstration
hey guys, I have an assignment that has the following requirements:
1. Write a class Line which represents a line in 2D
2. Two constructors: one with slope and intercept
one with (x1, y1) (x2, y2)
3. Member function findY(double) which for a given line
takes an xvalue and returns the yvalue
4. Write short main program which exercises the class and
show output
Below is what I did...I would appreciate any suggestions or comments about code, and if you think this is enough for the given requirements. Thanks,
axon
Code:
/* Author:
* Class: CS201
* Date: 09.08.03
* Assgn: Homework 0
* System: g++ and MSVC++
*/
#include <iostream>
using namespace std;
class Line
{
public:
//constructors
Line( double newSlope, double newIntercept );
Line( double newx1, double newy1, double newx2, double newy2 );
void output1(); //output for slope and yintercept
void output2(); //output for the coordinates
double findY(double x); // find ycoord from given xcoord
private:
double slope;
double intercept;
double x1, y1, x2, y2;
};
//
int main()
{
double x = 0;
double y = 0;
Line slopeAndIntercept(1, 2), coordinates(2, 4, 3, 1);
slopeAndIntercept.output1();
coordinates.output2();
x = 12;
cout << "\nCalculating ycoordinate when x = 12: " << endl;
y = slopeAndIntercept.findY(x);
cout << "When x = 12, y = " << y << endl;
return 0;
}
//
//defining functions and constructors
Line::Line( double newSlope, double newIntercept )
: slope(newSlope), intercept(newIntercept){}
Line::Line( double newx1, double newy1, double newx2, double newy2 )
: x1(newx1), y1(newy1), x2(newx2), y2(newy2){}
void Line::output1(){
cout << "Initializing slope of line to: " << slope << endl;
cout << "Initializing yintercept to: " << intercept << endl;
}
void Line::output2(){
cout << "\n( x1, y1 ) = ( " << x1 << ", " << y1 << " )" << endl;
cout << "( x2, y2 ) = ( " << x2 << ", " << y2 << " )" << endl;
}
double Line::findY(double x)
{
return (slope*x + intercept);
}

I would consider not storing the x1, y1, x2, and y2 that you get from the second constructor. Instead, it would make more sense to me to use it to figure out the slope and yintercept, then store those.
With your current code, try calling coordinates.findY(x). It will give you a crazy number because you don't initialize slope or intercept in your second constructor. It is nice to see that you are using initialization lists, but you have to remember to initialize all member variables on construction, not just the ones passed in.