what are the really small numbers from? C++ class

Question

I know I should include a "get_Diameter()" function in the class, so as to access the private data member, but I haven't been able to figure out where the really small numbers come from.

(Can ignore the Rectangle stuff - its a circle problem)

Here is the driver code:

// classes example
#include <iostream>
using namespace std;

#include "rect2.h"
#include "roughCirc.h"

int main () {
  Rectangle rect (3,4);
  Rectangle rectb;
  cout << "rect area: " << rect.area() << endl;
  cout << "rectb area: " << rectb.area() << endl;
  cout << " " << endl;

  Circle circ (1.3);
  cout << "circle area: " << circ.area() << endl;

  Circle circB;
  cout << "circle area: " << circB.area() << endl;
  return 0;
}
/*
g++ -o main2 main2.cpp rect2.cpp roughCirc.cpp 
*/

Class: roughCirc.h

class Circle {
    double diameter;
  public:
    Circle (double);
    Circle ();
    double area (void);
};

and roughCirc.cpp

#include <iostream>
using namespace std;

#include "roughCirc.h"

Circle::Circle (double) {
    diameter = 1.1212;
}

Circle::Circle () {
    diameter = 32.42;
}

double Circle::area(void) {
    double tmp = 3.1416 * 0.25 * diameter*diameter;
    cout << "diameter is: " << diameter << " and area is: " << tmp << endl;
}

and the output;

X@X:X$ ./main2
rect area: 12
rectb area: 25

circle area: diameter is: 1.1212 and area is: 0.987318
3.03428e-86
circle area: diameter is: 32.42 and area is: 825.5
3.03428e-86

Not sure it matters, but I have latest and greatest packages from Debian stable. Command line is at bottom of driver file.

You need to turn up your compiler warnings. `double Circle::area(void)` doesn't return anything even though you say it does. — NathanOliver, May 02 '18 at 21:20
TBH they may be the greatest, but if they are from Debian stable they aren't the latest for sure. — Matteo Italia, May 02 '18 at 21:23
And if you feel like being a jerk to your code or have a mystery bug , add in `-pedantic` to see if it picks off any of the little, normally insignificant details. — user4581301, May 02 '18 at 21:31
Your code is evil. The two constructors set the diameters to different values. The constructor that uses a parameter doesn't use the parameter. Evil. — Thomas Matthews, May 02 '18 at 22:41
yeah, it was put together quickly and the overloading was watched apparently very well... — nate, May 03 '18 at 01:35

score 5 · Accepted Answer · answered May 02 '18 at 21:21

Your function is declared to return a double

double Circle::area(void) {
    double tmp = 3.1416 * 0.25 * diameter*diameter;
    cout << "diameter is: " << diameter << " and area is: " << tmp << endl;
}

yet you have no return statement which returns a double. So this line

cout << "circle area: " << circB.area() << endl;

will invoke undefined behavior while outputting .area(). Instead you should return the result of your calculation

double Circle::area() {
    double tmp = 3.1416 * 0.25 * diameter*diameter;
    cout << "diameter is: " << diameter << " and area is: " << tmp << endl;
    return tmp;
}

what are the really small numbers from? C++ class

1 Answers1