Visual studio помогите с заданием

 #include <iostream>  
#include <valarray> 
#include <vector>

using namespace std;

size_t length(const char* prompt) { 
    size_t value{}; 
    while (!value) { 
        cout << prompt; 
        cin >> value; 
        cin.ignore(0x1000, '\n'); 
    } 
    return value; 
}

double average(const valarray<int>& va) { 
    return static_cast<double>(va.sum()) 
        / static_cast<double>(va.size()); 
}

int main() { 
    const auto rows = length("Rows: "); 
    const auto cols = length("Columns: "); 
    vector<valarray<int>> matrix(rows, valarray<int>(cols)); 
    puts("Input matrix..."); 
    for (auto& row : matrix) { 
        for (auto& value : row) { 
            cin >> value; 
        } 
    } 
    cout.put('\n'); 
    const auto avg = average(matrix[1]); 
    cout << "Average: " << avg << '\n'; 
    system("pause > nul"); 
}