Issue turning int array into matrix class to complete operator-overloading - c++

Question

I'm trying to multiply 2 matrices together using operator-overloading but I'm getting an error when trying to convert my int array into my matrix class in order to use it. I'm not sure how to fix these errors
#include <iostream>
using namespace std;
struct matrix{
int array[4][4];
public:
void make(int A[][4], int size) {
for (int x = 0; x < size; x++) {
for (int y = 0; y < size; y++) {
array[x][y] = A[x][y];
}
}
}
void operator*(matrix m) {
int output[4][4];
for (int x = 0; x < 4; x++){
for (int y = 0; y < 4; y++){
array[x][y] = (array[x][y] * m.array[x][y]);
}
}
for (int x = 0; x < 4; x++) {
for (int y = 0; y < 4; y++) {
cout << output[x][y] << " ";
}
cout << endl;
}
}
};
int main(){
matrix m1, m2;
int a[4][4] = {{1,2,3,4},{5,6,7,8},{9,10,11,12},{13,14,15,16}};
//int c[3][3] = {{1,2,3},{4,5,6},{7,8,9}};
m1.make(a[4][4], 4);
m2.make(a[4][4], 4);
m1*m2;
return 0;
}

Answer 1

There are two problem with your code:-
m1.make(a[4][4], 4); // should be m1.make(a, 4); make is expecting a 2D array you are passing an integer
In the operator *function
array[x][y] = (array[x][y] * m.array[x][y]); // your should assign to output[x][y] here

Answer 2

You are not using the corect syntax.
int main(){
matrix m1, m2;
int a[4][4] = {{1,2,3,4},{5,6,7,8},{9,10,11,12},{13,14,15,16}};
//int c[3][3] = {{1,2,3},{4,5,6},{7,8,9}};
// these are not good, you try to pass a single int, and it is past the
// end of a.
//m1.make(a[4][4], 4);
//m2.make(a[4][4], 4);
// try this instead:
m1.make(a, 4);
m2.make(a, 4);
m1*m2;
return 0;
}
Multiplying is a binary operator that takes in 2 matrices, and outputs a third one with the result.
class matrix
{
// note the friend modifier, which indicates this fonction is a not a member
// of the class, and can access all of its private members.
friend matrix operator*(const matrix& m, const matrix& n)
{
matrix result;
for (int x = 0; x < 4; x++)
for (int y = 0; y < 4; y++)
result.array[x][y] = (m.array[x][y] * n.array[x][y]);
// your formula does not seem quite right here...
// I'll let you fix it.
return result;
}
Here is the correct syntax for make() to accept an int[4][4] array:
void make(int (&A)[4][4]) {
for (int x = 0; x < 4; x++) {
for (int y = 0; y < 4; y++) {
array[x][y] = A[x][y];
}
}
}
Why don't you have a constructor instead of make?
class matrix{
private:
int array[4][4];
public:
// you want to initialize your data, always (well, almost always, but
// this is the kind of data that always applies to)...
matrix()
{
for (int x = 0; x < 4; x++)
for (int y = 0; y < 4; y++)
array[x][y] = 0;
}
explicit matrix(const int(&a)[4][4])
{
for (int x = 0; x < 4; x++)
for (int y = 0; y < 4; y++)
array[x][y] = a[x][y];
}
matrix& operator=(const int(&a)[4][4])
{
return *this = matrix(a);
}
matrix& operator=(const matrix& m)
{
for (int x = 0; x < 4; x++)
for (int y = 0; y < 4; y++)
array[x][y] = m.array[x][y];
return *this;
}
// ...
};
Then main() becomes:
int main(){
matrix m1, m2;
int a[4][4] = {{1,2,3,4},{5,6,7,8},{9,10,11,12},{13,14,15,16}};
matrix m1(a);
matrix m2(a);
matrix product = m1 * m2;
return 0;
}