Hey, so this is the current method:

void move(int &movesMade, std::pair<int,int> &currentPos, vector<std::pair<int,int>> &visitedFields, std::vector<int> &lastUsedRule, std::vector< std::pair<int,int> > &longestRoute, rulebook &rules ) {
     if(lastUsedRule.size() >= 1) {
        if (currentPos.first == 0 && currentPos.second == 0 && lastUsedRule.at(0) == (rules.getPossibleMoves() - 1) ) {
            return;
        }
    }

When I try to run the whole program, it throws an out of bounds exception. The thing is: I know that the exception occurs because of "lastUsedRule.at(0)" inside of the if-condition, because std::vector throws it, if the given parameter for the at-function is greater or equal to the size of the vector. The vector is empty, so its size is 0 and so it produces an exception. To avoid exactely this situation the programm checks whether the size is greater than 0 - Still it throws the exception. I don't understand it, to be honest.

What can I change to get this function working? Thanks in advance.

EDIT: Forgot the rest of the code (Here is the task I'm working on https://www.reddit.com/r/dailyprogrammer/comments/6dgiig/20170526_challenge_316_hard_longest_uncrossed/ ):

#include <cstdlib>
#include <iostream>
#include <vector>
#include <array>
#include <utility>
#include <algorithm>

using namespace std;


struct rulebook {
    std::vector< std::pair<int,int> > moves {
        { std::pair<int,int>{1,2} }, 
        { std::pair<int,int>{1,-2} },
        { std::pair<int,int>{-1,2} },
        { std::pair<int,int>{-1,-2} },
        { std::pair<int,int>{2,1} },
        { std::pair<int,int>{2,-1} },
        { std::pair<int,int>{-2,1} },
        { std::pair<int,int>{-2,-1} }
    };
    const int n;

    rulebook(int range) : n(range) {};
    int getN() { return n; };
    int getPossibleMoves() {
        return moves.size();
    }
};

bool outOfBounds(std::pair<int,int> currentPos, std::pair<int,int> destination, int n) {

}

bool illegalMove (std::pair<int,int> currentPos, std::pair<int,int> destination, vector<std::pair<int,int>> visitedFields, rulebook rules) {

}

    void move(int &movesMade, std::pair<int,int> &currentPos, vector<std::pair<int,int>> &visitedFields, std::vector<int> &lastUsedRule, std::vector< std::pair<int,int> > &longestRoute, rulebook &rules ) {
         if( !lastUsedRule.empty() ) {
            if (currentPos.first == 0 && currentPos.second == 0 && lastUsedRule.at(0) == (rules.getPossibleMoves() - 1) ) {
                return;
            }
        }

    /*if (movesMade > 0 && !lastUsedRule.empty()) {
        if ( lastUsedRule.at(movesMade) == rules.getPossibleMoves() ) {
            movesMade--;
            currentPos.first = visitedFields.at(movesMade).first;
            currentPos.second = visitedFields.at(movesMade).second;
            visitedFields.pop_back();
            lastUsedRule.pop_back();
            return;
        }
    }
    if ( movesMade == lastUsedRule.size() ) {
        int temp = 0;
        lastUsedRule.push_back(temp);
    }*/

}

int main(int argc, char** argv) {
    int n;
    int movesMade = 0;
    pair<int, int> position = {0,0};
    std::vector< std::pair<int,int> > visitedFields;
    std::vector<int> lastUsedRule;
    std::vector< std::pair<int,int> > longestRoute;

    visitedFields.push_back(position);
    cout << "Enter the board length:" << endl;
    cin >> n;
    rulebook rules(n);

    move(movesMade, position, visitedFields, lastUsedRule, longestRoute, rules);

    return 0;
}

EDIT2: I know that there are also errors in the rest of the given method, probably because of the same reasons. I commented everything out but the snippet above.