displaying problem

Hi,
I have the following problem ( triangle of sides a,b,c)

Write a void function that uses five parameters: 3 values are the length of the edges of the triangle, and 2 are reference parameter that compute the area and perimeter.
Make the function robust.
Note that not all combination of a,b,c produce a triangle.
the function should produce correct results for legal data and reasonable results for illegal combination.

This is what I wrote below.
The problem I have is that when I enter bad combination for the edges of the triangles, instead of just displaying "bad combination, it continues and compute the area and perimeter (even though the data are illegal.

Code:

---


#include<iostream>
#include<cmath>

using namespace std;

int main() //driver program
{
double area,perimeter;
int finish,a,b,c;
void compute_area(double&,double&,double,double,double);
a=8;
b=8;
c=30;
compute_area(area,perimeter,a,b,c);

cout << "The area of a triangle with sides of length " << a
        << " , " << b << " and " << c << " is " << area <<
        "and the  perimeter is "<<perimeter<< endl;


cin>>finish;// to keep output window open

return 0;
}//end main


// function

void compute_area (double& area, double& perimeter, double a, double b, double c) {
  double s;
   
    if( (a<(b+c))||(b<(a+c))||(c<(b+a)) )
    { cout<<"bad combination!"<<endl;
      return;
    }
  else
  {
  s = (a + b + c)/ 2.0;// semiperimeter
  area = sqrt (s*(s-a)*(s-b)*(s-c)); // area triangle
  perimeter=a+b+c;
  }
  return;
}

---

Thank you.
B

You should put this -

void compute_area(double&,double&,double,double,double) ;

before int main().

You shouldn't print the result if there's an error. Maybe return a bool and only print if it's true?

Code:

---

#include <iostream>
#include <cmath>

using namespace std;

// the way you had it was okay, but this is probably better
bool compute_area(double&, double&, double, double, double);

int main()
{
    double area,perimeter;

    // always initialize if you can
    int a = 8;
    int b = 8;
    int c = 30;

    if (compute_area(area,perimeter,a,b,c))
    {
        cout << "The area of a triangle with sides of length " << a
            << " , " << b << " and " << c << " is " << area <<
            "and the  perimeter is "<<perimeter<< endl;
    }

    cin.get(); // better way to keep the window open

    return 0;
}

bool compute_area (double& area, double& perimeter, double a, double b, double c)
{
    double s;

    if( (a<(b+c))||(b<(a+c))||(c<(b+a)) )
    {
        cout<<"bad combination!"<<endl;
        return false;
    }
    else
    {
        s = (a + b + c)/ 2.0;// semiperimeter
        area = sqrt (s*(s-a)*(s-b)*(s-c)); // area triangle
        perimeter=a+b+c;
    }

    return true;
}

---

Quote:

---

Originally Posted by Hikaru

You shouldn't print the result if there's an error. Maybe return a bool and only print if it's true?

Code:

---

#include <iostream>
#include <cmath>

using namespace std;

// the way you had it was okay, but this is probably better
bool compute_area(double&, double&, double, double, double);

int main()
{
    double area,perimeter;

    // always initialize if you can
    int a = 8;
    int b = 8;
    int c = 30;

    if (compute_area(area,perimeter,a,b,c))
    {
        cout << "The area of a triangle with sides of length " << a
            << " , " << b << " and " << c << " is " << area <<
            "and the  perimeter is "<<perimeter<< endl;
    }

    cin.get(); // better way to keep the window open

    return 0;
}

bool compute_area (double& area, double& perimeter, double a, double b, double c)
{
    double s;

    if( (a<(b+c))||(b<(a+c))||(c<(b+a)) )
    {
        cout<<"bad combination!"<<endl;
        return false;
    }
    else
    {
        s = (a + b + c)/ 2.0;// semiperimeter
        area = sqrt (s*(s-a)*(s-b)*(s-c)); // area triangle
        perimeter=a+b+c;
    }

    return true;
}

---

---

Yes I thought about that but the function must be a VOID type !


B

>> Yes I thought about that but the function must be a VOID type !

That's a bad restriction! It doesn't "Make the function robust", does it?
Set the area and the perimiter values to -1 when it fails.

Code:

---

compute_area( area, perimeter, a, b, c );

if ( (area == -1) || (perimiter == -1) ) // Technically && but whatever
{
        std::cout<< "ERROR!";
}
else
{
        std::cout<< "OK!!";
}

---

But, IMO a bool would be better

Quote:

---

Yes I thought about that but the function must be a VOID type !

---

Ah, gomen. :o A better way would throw an exception.

Code:

---

#include <iostream>
#include <stdexcept>
#include <cmath>

using namespace std;

// the way you had it was okay, but this is probably better
void compute_area(double&, double&, double, double, double);

int main()
{
    double area,perimeter;

    // always initialize if you can
    int a = 8;
    int b = 8;
    int c = 30;

    try
    {
        compute_area(area,perimeter,a,b,c);
        cout << "The area of a triangle with sides of length " << a
            << " , " << b << " and " << c << " is " << area <<
            "and the  perimeter is "<<perimeter<< endl;
    }
    catch (const std::invalid_argument& e)
    {
        std::cerr << e.what() << '\n';
    }

    cin.get(); // better way to keep the window open

    return 0;
}

void compute_area (double& area, double& perimeter, double a, double b, double c)
{
    double s;

    if( (a<(b+c))||(b<(a+c))||(c<(b+a)) )
    {
        throw std::invalid_argument("Bad combination");
    }
    else
    {
        s = (a + b + c)/ 2.0;// semiperimeter
        area = sqrt (s*(s-a)*(s-b)*(s-c)); // area triangle
        perimeter=a+b+c;
    }
}

---

That's probably not allowed. The only other way I can think of is a global variable to flag errors. It's a bad option though. I only mention it because it seems like your teacher is forcing that kind of error handling method.

Code:

---

#include <iostream>
#include <stdexcept>
#include <cmath>

using namespace std;

namespace
{
    bool error = false;
}

// the way you had it was okay, but this is probably better
void compute_area(double&, double&, double, double, double);

int main()
{
    double area,perimeter;

    // always initialize if you can
    int a = 8;
    int b = 8;
    int c = 30;

    compute_area(area,perimeter,a,b,c);

    if (!error)
    {
        cout << "The area of a triangle with sides of length " << a
            << " , " << b << " and " << c << " is " << area <<
            "and the  perimeter is "<<perimeter<< endl;
    }

    cin.get(); // better way to keep the window open

    return 0;
}

void compute_area (double& area, double& perimeter, double a, double b, double c)
{
    double s;

    if( (a<(b+c))||(b<(a+c))||(c<(b+a)) )
    {
        std::cerr << "Bad combination\n";
        error = true;
    }
    else
    {
        s = (a + b + c)/ 2.0;// semiperimeter
        area = sqrt (s*(s-a)*(s-b)*(s-c)); // area triangle
        perimeter=a+b+c;
    }
}

---

Or my idea (post #5), with the -1's with this function -

Code:

---

void compute_area (double& area, double& perimeter, double a, double b, double c)
{
    if( (a<(b+c)) || (b<(a+c)) || (c<(b+a)) )
    {
        area = -1;
        perimiter = -1;
    }
    else
    {
        double s;

        s    = (a + b + c)/ 2.0; // semiperimeter
        area = sqrt (s*(s-a)*(s-b)*(s-c)); // area triangle        perimeter=a+b+c;
    }
}

---