santa's list, C++ (vc++)

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#include <iostream>
#include <cstdlib> // <stdlib.h>
#include <vector>
#include <ctime> // <time.h>

// using namespace std;

constexpr auto SIZE = 20 ; // 10;
constexpr auto low_bound = 0;
constexpr auto up_bound = 20;

int main() {

std::srand(time(nullptr/*NULL*/));///Instructor told me to use this so don't hate
    std::vector<int> listo;

std::cout << "Here is Santa's list!\n";

for(int i = 0; i < SIZE /*20*/ ; i++) {

// listo.push_back(rand() % 20 + 1);///Fills vector with 20 random integers
        listo.push_back( std::rand() % (up_bound-low_bound) + low_bound + 1 ) ;

std::cout << listo[i] << " ";///Prints the vector
    }
    std::cout << '\n' ; // "\n";
    // system("PAUSE");

/*http://www.cplusplus.com/reference/vector/vector/?kw=vector
    err is just a copy of listo*/

std::cout << "\nMaybe Santa made a mistake! Here is the revised version. \n";

// for each number in the vector
    // since we are erasing duplicate numbers, the size may become less than SIZE
    // size_t: http://en.cppreference.com/w/cpp/types/size_t
    for( std::size_t i = 0; i < listo.size() /*20*/ ; ++i ) {

// check if any number after this number is a duplicate
        // note: we do not have to look at numbers before this number
        //       duplicates of earlier numbers have already been taken care of
        for( std::size_t n = i+1;  n < listo.size() ; ++n ) {

if( listo[n] == listo[i] ) { // found a duplicate number

listo.erase( listo.begin() + n );///deletes value
            }
        }
    }

for( std::size_t i = 0; i < listo.size() ; ++i ) {

std::cout << listo[i] << ' ' ;///prints off revised vector
        // cout << " ";
    }
    std::cout << '\n' ;
}

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Compilation time: 6,82 sec, absolute running time: 0,22 sec, absolute service time: 7,05 sec