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    <p>This has nothing to do with "calling object C".</p> <p>The first version </p> <pre><code>Matrix C = A * B; </code></pre> <p>uses <em>constructor(s)</em> or class <code>Matrix</code> to initialize new object <code>C</code>.</p> <p>The second version </p> <pre><code>C = C * C; </code></pre> <p>uses <em>assignment</em> operator of class <code>Matrix</code> to assign new value to an existing object <code>C</code>.</p> <p>You managed to screw up the assignment operator declaration/implementation somehow (which you don't show in the code you posted), which is why the second version does not compile.</p> <p>There are problems with your <code>operator *</code> declaration as well. Even if you want to have it as class member, a more meaningful way to declare it would be </p> <pre><code>Matrix Matrix::operator* (const Matrix&amp; B) const { ... </code></pre> <p>Note how <code>const</code> qualifiers are placed. </p> <p><strong>EDIT:</strong> So, here's your problem. Your assignment operator is completely broken.</p> <p>Firstly, you declared your assignment operator as</p> <pre><code>Matrix Matrix::operator=(Matrix&amp; B) </code></pre> <p>This operator cannot accept temporary objects on the right-hand side because you failed to declare the parameter as <code>const</code>. Non-const references cannot be bound to temporary objects. And in <code>C = C * C</code> the right-hand side of assignment is actually a temporary object produced by <code>*</code>operator.</p> <p>Redeclare your assignment operator as </p> <pre><code>Matrix &amp;Matrix::operator=(const Matrix&amp; B) </code></pre> <p>Note, it accepts a <code>const</code> reference and returns a reference.</p> <p>Secondly, your assignment operator is supposed to assign to <code>*this</code>, not to some standalone temporary object. And it is supposed to return a reference to <code>*this</code>. In other words, the implementation should be something along the lines of</p> <pre><code>Matrix &amp;Matrix::operator=(const Matrix&amp; B){ // Resize `*this` to match the size of `B` for(int i = 0; i &lt; M; i++){ for(int j = 0; j &lt; N; j++){ this-&gt;data[i*N+j] = B(i,j); } } return r; } </code></pre>
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    1. POOverloaded operator C++: Object = Object * Object
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    1. COIf the method is const, how would it create a new matrix? Or modify an existing one?
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    2. CO@Billy Jake O'Connor: This is not "assignment operator". What you posted is a *copy constructor*. It has absolutely nothing to do with assignment operator. Your problem is in *assignment operator*. Do you understand the difference between *copy constructor* and *assignment operator*??? Assignment operator is called as `operator =`. What did you do to it?
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    3. CO@Smac89: What do you see as a problem with creating new matrix in a `const` method??? `const` method only prevents you from modifying `*this` and nothing else. The OP does not modify (and does not need to modify) `*this` in `operator *`, so it is perfectly logical to declare the method `const`.
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