C++: memory-management issue and new-operator

Question

I'm new to C++ (which is probably obvious based on below code ...) and don't manage to solve the following problem: when running below program, (*c).print(); prints values that are obviously wrong but I don't understand why. Since I haven't fully understood memory-management, I assume the problem is related to that and I hope the solution will give me a better understanding (e.g., my understanding is, that when creating an array using new, the elements of the array don't have to be created using new[?]. Specifically, Complex* aa = new Complex[3]; should be sufficient). Thanks in advance!

Console-output with the wrong data highlighted

#include <cstdlib>
#include <iostream>

using namespace std;

class Complex {
    public:
        double real;
        double imag;
        
    public:
        Complex() {
            real = 0.0;
            imag = 0.0;
        }

    public:
        Complex(double real, double imag) {
            Complex::real = real;
            Complex::imag = imag;
        }
    
    public:
        Complex operator + (const Complex& other) {
            return Complex(real + other.real, imag + other.imag);
        }
    
    public:
        void print() {
            if (imag >= 0) {
                cout << real << " + " << imag << " i\t\t";
            } else {
                cout << real << " " << imag << " i\t\t";
            }
        }
};

class triMatrix {
    
    public:
        Complex** mat;
        int dim;
    
    public:
        triMatrix(int dim, Complex* array) {
            triMatrix::dim = dim;
            mat = new Complex*[dim];
            int k = 0;
            for (int i = 0; i < dim; ++i) {
                mat[i] = new Complex[dim];
                for (int j = 0; j <= i; ++j) {
                    mat[i][j] = array[k];
                    ++k;
                }
            }
        }
    
    public:
        ~triMatrix() {
            for (int i = 0; i < dim; ++i) {
                delete[] mat[i];
            }
            delete[] mat;
        }
        
    public:
        triMatrix operator + (const triMatrix& other) {
            Complex *c = new Complex[(dim + 1) * dim / 2];
            triMatrix *sum = new triMatrix(dim, c);
            for (int i = 0; i < dim; ++i) {
                for (int j = 0; j < dim; ++j) {
                    sum->mat[i][j] = mat[i][j] + other.mat[i][j];
                }
            }
            (*sum).print();
            return *sum;
        }
        
    public:
        void print() {
            for (int i = 0; i < dim; ++i) {
                for (int j = 0; j < dim; ++j) {
                    mat[i][j].print();
                }
                cout << endl;
            }
        }
};

int main () {
    
    Complex* aa = new Complex[3];
    aa[0] = Complex(1.2, 0.2);
    aa[1] = Complex(3.2, -0.2);
    aa[2] = Complex(-12.4, 0);
    
    triMatrix *a = new triMatrix(2, aa);
    (*a).print();
    
    Complex* bb = new Complex[3];
    bb[0] = Complex(-6.3, 0);
    bb[1] = Complex(2.3, 0);
    bb[2] = Complex(4.3, -1.2);
    
    triMatrix *b = new triMatrix(2, bb);
    (*b).print();
    
    cout << sizeof(triMatrix) << endl;
    
    triMatrix *c;
    c = (triMatrix*) malloc(sizeof(triMatrix));
    *c = *b + *a;

    (*c).print();
    
    (*a).print();
    (*b).print();
}