program won't work

Why doesn't the following code work when we uncomment the function comp(double& t)? Isn't the funtion supposed to get called when we do, comp c = n?

Code:

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#include<iostream>
#include<conio.h>
#include<ctype.h>

class comp
{
        double r,i;

public:
        comp (double rr = 0, double ii = 0)
        {
                r = rr;
                i = ii;
        }

        /*comp(double &t)
        {
                r = t;
                i = i;
        }*/
};


int main()
{
        comp a(1.9,4.9), b(0.9,1.9);
        double n = 0.1;
        comp c = n;
}

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Quote:

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Originally Posted by juice

Why doesn't the following code work when we uncomment the function comp(double& t)? Isn't the funtion supposed to get called when we do, comp c = n?

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Because what you're trying, needs an assignment operator.
Like this:

Code:

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void operator=(const double& t)
{
    //Your code
}

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Quote:

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Originally Posted by manasij7479

Because what you're trying, needs an assignment operator.

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an assignment operator won't work either..

Quote:

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Originally Posted by juice

an assignment operator won't work either..

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Really ? ...
Then, perhaps you can enlighten me, why it is called an assignment operator !

P.S: It works..
Here is a small example:

Code:

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class foo
{
public:
    int x;
    void operator=(int n){x=n;};
    foo(){};
};

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copy the code into your compiler, uncomment the function, introduce an overloaded assignment operator and check it out for yourself.

You can use this assignment operator

Code:

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void operator= (comp &t)
{
r = t;
}

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Quote:

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Originally Posted by juice

copy the code into your compiler, uncomment the function, introduce an overloaded assignment operator and check it out for yourself.

You can use this assignment operator

Code:

---

void operator= (comp &t)
{
r = t;
}

---

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That is simply because the call becomes ambiguous with the constructor (as there are default values).
That being the case, you don't even need an operator. The constructor will automatically be called for the assignment.(I don't know if that behaviour is standard, but my compiler seems to be satisfied.)

Your default arguments are confusing things here. How is a single argument instantiation of the class going to resolve between the two constructors? Does it call the first constructor and use a default argument of 0 for the second, or does it call the single argument constructor? If you get rid of the default arguments, the code should compile.

But when we say comp c = n, isn't a copy constructor supposed to get invoked..

If n was another comp object then it would call the copy constructor. But, n is a double and that particular statement gets converted into a call to the constructor that expects a double argument (of which you had two available hence the confusion).

Code:

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comp a;
comp b = a;  // comp b(a)

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Here, since b and a are the same type, the copy constructor would be called.

Code:

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double n = 9.0;
comp a = n;  // comp a(n)

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Here, since n is a double, it tries to resolve which constructor to call based on ones that accept a double parameter. You have two of them, the one with the default arguments and the one with the one double argument. Either are possible options and the compiler complains.