//program asks for two sides of a triangle and computes the hypotenuse, assuming a right triangle
//this program illustrates writing to a text file from within a function
//by passing the file variable to the function as a parameter
//If done, this way, main handles the opening and closing of the file.
//the program also shows how the output function can write to the std ostream cout object
//ofstream is a special case of ostream

#include <iostream>
#include <fstream>
#include <cmath>
using namespace std;

void inputSides( float &, float &);     //input two side of a right triangle
void validateInput (float &);  //input validation loop
void outputTriangle( ostream &,float,float);   //output sides of right triangle and its hypotenuse
float calcHypotenuse( float, float);

int main()
{
    ofstream outFile;
    float leg1, leg2, hypotenuse;   //triangle legs
    char answer;                    //for user response to do another case
    outFile.open("HYP.TXT");
    do
    {
        inputSides(leg1, leg2);
        outputTriangle(outFile, leg1, leg2);
        outputTriangle(cout, leg1,leg2);
        cout << "Do another?  (Y/N) ";
        cin >> answer;
    } while ( answer == 'Y'|| answer == 'y');
    outFile.close();

    return 0;
}

void inputSides( float &a, float &b)
{
    cout << "Enter first leg of a right triangle. ";
    cin >> a;
    validateInput(a);
    cout << "Enter second leg of a right triangle. ";
    cin >> b;
    validateInput(b);
}   //end inputSides

//validation function ensures positive entries
void validateInput(float &x)
{
    while (x <=0)
    {
        cout << "Input must be positive.  Re-input the side ";
        cin >> x;
    }
}   //end validateInput

//outputTriangle first calculates the hypotenuse, probably not the best design.
//main() should do this, but I wanted to show how a function can call another function!
void outputTriangle(ostream & outf, float a, float b)
{
    float hypotenuse;
    hypotenuse = calcHypotenuse(a, b);
    outf << "A right triangle with legs " << a << " and " << b;
    outf << " has hypotenuse " << hypotenuse << endl;
}

float calcHypotenuse(float a, float b)
{
    return sqrt(a*a + b*b);
}