#include <iostream>

#include <fstream>

#include <vector>

#include <string>

// Get an integer from the user. Note that std::stoi can

// throw a std::invalid_argument exception if the user's

// input is not an integer, and it can throw std::out_of_range

// if the string is a valid integer but outside the range of

// a C++ int on this platform.

int get_int() {

std::string input;

std::cin >> input;

int result = stoi(input);

return result;

}

int main() {

std::vector<int> a { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 };

try { // What possibly could go wrong?

int n = a.size();

std::cout << "Enter index in the range 0..." << n - 1 << ": ";

// Will user enter a valid integer value?

int i = get_int();

std::cout << "Index entered: " << i << '\n';

// Will the user's index be in the range of valid indices?

std::cout << "a[" << i << "] = " << a.at(i) << '\n';

}

catch (std::out_of_range&) {

std::cout << "Index provided is out of range\n";

}

catch (std::invalid_argument&) {

std::cout << "Index provided is not an integer\n";

}

catch (...) { // What have we forgotten?

std::cout << "Unknown error\n";

}

}