CODEWITHSUNDEEP
c++
impatient salmon
impatient salmon

Reputation: 23

(C++) multiplication wont give off expected results

hello :) so this is my first time writing a c++ program, im currently using code::blocks tho im pretty sure the issue ive got probably isnt related to the program at all but anyway...

i want to write a simple code, where two "boxes" are created and their volume is calculated and printed on the terminal. ive written this code on a single cpp file: 

#include<iostream>
using namespace std;

class Box
{
public:
    double length;
    double breadth;
    double height;

    Box(double l, double b, double h)
    {
      l=length;
      b=breadth;
      h=height;
    }
};

int main()
{
    double volume = 0.0;
    Box BoxA(2.0, 3.2, 6.0);
    Box BoxB(2.5, 4.0, 5.0);
    volume = BoxA.length * BoxA.breadth * BoxA.height;
    cout << "Box a volume = " << volume <<endl;
    volume = BoxB.length * BoxB.breadth * BoxB.height;
    cout << "Box b volume = " << volume <<endl;
    return 0;
}

so i build and run this thing, no errors but the results i get is this:

box a volume = -0

//and sometimes =0

box b volume = 0

but i dont understand what is wrong here. shouldnt the results be a=38.4 and b=50.0? what am i doing wrong here?

Upvotes: 1

Views: 101

Answers (3)

L. Scott Johnson
L. Scott Johnson

Reputation: 4382

Your constructor assigns values to the passed arguments.

Try this instead:

class Box
{
public:
    double length;
    double breadth;
    double height;

    Box(double l, double b, double h)
    {
      length=l;
      breadth=b;
      height=h;
    }
};

As others have mentioned, there are other improvements that can be made regarding initializer lists and the use of using, and the study of programming in general and c++ in particular is an ongoing journey, never a destination, but this is the direct fix for the immediate problem.

Upvotes: 3

MSalters
MSalters

Reputation: 179799

The usual way to write constructors is with initializer lists:

Box(double l, double b, double h) : length(l), breadth(b), height(h)
{
}

This prevent exactly the same error that you had, exchanging the argument and member. If you tried to write : l(length), the compiler would have told you straight away that l is not a member of Box.

You don't even need separate names with initializer lists:

Box(double length, double breadth, double height)  
    : length(length), breadth(breadth), height(height)
{ }

This does initialize Box::height with the argument height.

Upvotes: 3

Rohan Bari
Rohan Bari

Reputation: 7726

#include<iostream>

class Box
{
public:
    double length;
    double breadth;
    double height;

    Box(double l, double b, double h)
    {
        length = l; // assign to the member variables, not parameters
        breadth = b;
        height = h;
    }
};

int main(void)
{
    double volume = 0.0;

    Box BoxA(2.0, 3.2, 6.0);
    Box BoxB(2.5, 4.0, 5.0);

    volume = BoxA.length * BoxA.breadth * BoxA.height;
    std::cout << "Box a volume = " << volume << std::endl;

    volume = BoxB.length * BoxB.breadth * BoxB.height;
    std::cout << "Box b volume = " << volume << std::endl;

    return 0;
}

This is the refined version of your code. Note that you shouldn't use namespace std. That's a bad programming practice.

Upvotes: 2

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