Getting the maximum Pair Wise product C++ and the output is not always right with my code

Question

Problem to solve: given an array or sequence of numbers the goal is to find the Max number obtained by the multiplication of some 2 numbers in that sequence.

example of inputs and outputs

Input:
2
100000 90000

Correct output:
9000000000

Input:
3
1 2 3

Correct output:
6

My Solution: get the 2 Maximum numbers in the sequence given and multiply them my code works unless with one solution

My code

#include <vector> 
#include <iostream> 
#include <algorithm> 
using namespace std;
void print(std::vector<int> const& input)
{
    for (int i = 0; i < input.size(); i++) {
        std::cout << input.at(i) << '   ';
    }
}

int main()
{
   
    vector<int> seq;
    int n;

    // Read the nb of elements in vect
    cout << "please enter the number of elements in sequence"<<endl;
    cin >> n;

    // Read the vector 
    cout << "please enter the elements of the sequence"<<endl;
    for (int i = 0; i < n; i++)
    {
        int input;
        cin >> input;
        seq.push_back(input);
    }
    cout << "sequence you entered" << endl;
    print(seq);


    // Find the 1st max element 
    double FisrtMax=*max_element(seq.begin(), seq.end());
    cout <<endl<< "First Maximum Element is" << endl<< FisrtMax;

    // remove the found element
    std::vector<int>::iterator PosF = find(seq.begin(), seq.end(), FisrtMax);
    seq.erase(PosF);

    cout <<endl<< "sequence After removing the 1st maximum element" << endl;
    print(seq);


    // Find the 2nd max element
    double SecMax = *max_element(seq.begin(), seq.end());
    cout <<endl<< "Second Maximum Element is" << endl << SecMax;

    //multiply the 2 elements
    int total =  (FisrtMax * SecMax);
    cout <<endl<<"The Product of the 2 elemnts is  "<< total;

    return 0;
}

The Input :

please enter the number of elements in sequence
2
please enter the elements of the sequence
1000000
90000

The Output :

please enter the number of elements in sequence
2
please enter the elements of the sequence
1000000
90000
sequence you entered
10000002105376900002105376
First Maximum Element is
1e+06
sequence After removing the 1st maximum element
900002105376
Second Maximum Element is
90000
The Product of the 2 elements is  -2147483648

Answer 1

There are several mistakes in the code:

1. cout << ... << ' ' syntax tries to print three whitespace characters letters using a single-quote which accepts a single letter not multiple. Use " " instead.

2. The result produced can't be held by an integer, you need to define size_t (which expands into unsigned long long in most compilers).

Side Tips:

• In this syntax:

   for (int i = 0; i < input.size(); i++)
  

  You're trying to compare an integer to size_t (returned by size() member function of vector class object). Rather than that, declare i with size_t.

• In this syntax:

   std::vector<int>::iterator PosF = find(seq.begin(), seq.end(), FisrtMax);
  

  You don't need to define such long type std::vector<int>::iterator, use auto keyword here:

   auto PosF = find(seq.begin(), seq.end(), FirstMax);
  

---

Code redefined:

#include <vector>
#include <iostream>
#include <algorithm>

using namespace std;

void print(std::vector<size_t> const &input) {
    for (size_t i = 0; i < input.size(); i++)
        std::cout << input.at(i) << "   ";
}

int main(void) {
    vector<size_t> seq;
    int n;

    // Read the nb of elements in vect
    cout << "please enter the number of elements in sequence" << endl;
    cin >> n;

    // Read the vector
    cout << "please enter the elements of the sequence" << endl;

    for (int i = 0; i < n; i++) {
        int input;
        cin >> input;
        seq.push_back(input);
    }
    cout << "sequence you entered" << endl;
    print(seq);

    // Find the 1st max element
    double FisrtMax = *max_element(seq.begin(), seq.end());
    cout << endl
         << "First Maximum Element is" << endl
         << FisrtMax;

    // remove the found element
    auto PosF = find(seq.begin(), seq.end(), FisrtMax);
    seq.erase(PosF);

    cout << endl << "sequence After removing the 1st maximum element" << endl;
    print(seq);

    // Find the 2nd max element
    double SecMax = *max_element(seq.begin(), seq.end());

    cout << endl
         << "Second Maximum Element is" << endl
         << SecMax;

    //multiply the 2 elements
    size_t total = (FisrtMax * SecMax);
    
    cout << endl
         << "The Product of the 2 elements is  " << total;

    return 0;
}

---

Its Inputs:

please enter the number of elements in sequence
2
please enter the elements of the sequence
1000000
90000

It outputs:

sequence you entered
1000000   90000
First Maximum Element is
1e+06
sequence After removing the 1st maximum element
90000   
Second Maximum Element is
90000
The Product of the 2 elemnts is  90000000000

Edit: This program successfully works on OnlineGDB and the program was compiled with C++14 flag.