Помогите дописать код C++

#include <iostream>
#include <iomanip>
using namespace std;
unsigned length(const char* msg, unsigned limit = numeric_limits<unsigned>::max() - 1U) {
auto value = 0U;;
do {
cout << msg;
cin >> value;
cin.ignore(cin.rdbuf()->in_avail());
} while (value > limit);
return value;
}
int main() {
system("chcp 1251 > nul");
const auto limit = 10U;
int matrix[limit][limit]{};
auto n = length("Введите количество строк: ", limit);
auto m = length("Введите количество столбцов: ", limit);
for (auto i = 0U; i < n; ++i) {
for (auto j = 0U; j < m; ++j) {
cout << "matrix[" << i << "][" << j << "] >>> ";
cin >> matrix[i][j];
}
}
system("cls");
for (auto i = 0U; i < n; ++i) {
for (auto j = 0U; j < m; ++j) {
cout << ' ' << setw(4) << matrix[i][j];
}
puts("");
}
puts("");
size_t min_i, min_j, max_i, max_j;
for (auto i = 0U; i < n; ++i) {
min_i = max_i = i;
min_j = max_j = 0U;
for (auto j = 1U; j < m; ++j) {
if (matrix[i][j] < matrix[min_i][min_j]) {
min_i = i;
min_j = j;
}
if (matrix[i][j] > matrix[max_i][max_j]) {
max_i = i;
max_j = j;
}
}
swap(matrix[min_i][min_j], matrix[max_i][max_j]);
}
for (auto i = 0U; i < n; ++i) {
for (auto j = 0U; j < m; ++j) {
cout << ' ' << setw(4) << matrix[i][j];
}
puts("");
}
puts("");
auto sum = 0LL;
for (auto i = 0U; i < n; ++i) sum += matrix[i][i];
cout << "Сумма элементов на главной диагонали: " << sum << '\n';
system("pause > nul");
}