Simple Matrix addition in C++.

matrix_demo.cxx

#include <iostream>
#include <vector>

using std::vector;

// Represents a matrix with the contents stored in row major order.
struct Matrix {
	int numRows;
	int numColumns;
	vector<vector<int>> contents;
};

// Construct a Matrix from a list of rows.
Matrix ToMatrix(const vector<vector<int>>& contents) {
	return {contents.size(), contents[0].size(), contents};
}

// Add two matricies 'a' and 'b' together.
Matrix Add(const Matrix& a, const Matrix& b) {
	Matrix c;
	c.numRows = a.numRows;
	c.numColumns = b.numColumns;
	for (int r = 0; r < a.numRows; ++r) {
		vector<int> row;
		for (int c = 0; c < a.numColumns; ++c) {
			row.push_back(a.contents[r][c] + b.contents[r][c]);
		}
		c.contents.push_back(row);
	}
	return c;
}

// Write a Matrix to an output stream.
std::ostream& operator <<(std::ostream& os, const Matrix& a) {
	os << "Matrix {numRows = " << a.numRows
	   << ", numColumns = " << a.numColumns
	   << ", contents = [";
	for (const vector<int>& row : a.contents) {
		os << "[ ";
		for (int e : row) {
			os << e << " ";
		}
		os << "]";
	}
	os << "]";
	return os;
}

int main() {
	Matrix a = ToMatrix({{1,2,3},{4,5,6}});
	Matrix b = ToMatrix({{1,1,1},{2,2,2}});
	std::cout << Add(a,b) << std::endl;
}