C++でトレースを求める

1,2,3,
4,5,6,
7,8,9,

15

#include <iostream>

void show(double*, int, int);
double Fnorm(double*, int, int);
double trace(double*, int, int);

int main() {
	int m = 3, n = 3;
	double sum = 0;
	double* x;
	x = new double[m * n];

	for (int i = 0; i < m * n; i++) {
		x[i] = i + 1;
	}
	show(x, n, m);
	std::cout << std::endl;

	std::cout << trace(x, n, m);


}
double Fnorm(double* x, int n, int m) {
	double norm = 0;

	for (int i = 0; i < n * m; i++) {
		norm += std::pow(x[i], 2);
		//std::cout << norm << std::endl;

	}
	std::cout << std::endl;

	return std::sqrt(norm);
}
void show(double* x, int n, int m) {
	int count = 0;
	for (int i = 0; i < m * n; i++) {
		count += 1;
		std::cout << x[i] << ",";
		if (count == m) {
			std::cout << std::endl;
			count = 0;
		}
	}
}
double trace(double* x, int n, int m) {
	int sum = 0, pos = 0;
	if (m != n) {
		std::cout << "error" << std::endl;
		return 0;
	}
	else {

		for (int i = 0; i < m * n; i++) {
			if (pos == i) {
				sum += x[i];
				pos += n + 1;
			}
		}
	}
	return sum;
}