checking if given vector contains already elements of pair in c++ -

let suppose have following pairs

0 -1  0 -2  0 -3  1- 2 2 -3 3- 4 2 -4 4- 5 5 -6 

i insert pairs vector , should have each element 1 times , instance start empty vector :

0-1 inserted checking 0-2 , there exist 0, not 2, 0-2 inserted, have

0-1 0-2 

now 0-3 , 3 not in list, can insert

0-1  0-2 0-3 

now lets consider 1-2 , of course have both of them , skip, let consider 2-3, again can skip, 3-4 , 3 exist not 4, can insert 3-4 , after inserting of 4 , 4 exist,so reject 2-4 comes 4-5 , 5-6, have following list

0-1  0-2 0-3 3-4  4-5 5-6 

i have following code

#include<iostream> #include<vector> #include<set> #include<algorithm> using namespace std; struct edge {     int a, c;     float weight;//edge  a-c  has weight     bool operator() (edge x, edge y)     {         x.weight < y.weight;      } }; int noncyclical_sum(vector<edge>s) {     int total = 0;     std::vector<std::pair<int, int>>  b;     auto m = make_pair(s[0].a, s[0].c);     b.push_back(m);     total = total + s[0].weight;     vector<edge>::iterator it;     (int = 1; < s.size(); i++)     {         auto m = make_pair(s[i].a, s[i].c);         //if (find(b.begin(), b.end(), s[i].a) != b.end() && find(b.begin(), b.end(), s[i].c) != b.end())              if (find(b.begin(), b.end(), m.first) != b.end() && find(b.begin(), b.end(), m.second) != b.end())             {             continue; //both element in  vector         }                 else         {              b.push_back(m);             total = total + s[i].weight;                     }          std::vector<std::pair<int, int>>::iterator ii;         (ii = b.begin(); ii != b.end(); ii++)             cout << ii->first << "  " << ii->second;              }  } int main() {        return 0; } 

at first time , have pushed first pair, starting second one, checking if @ same time both element in vector, rejecting pairs , continue, otherwise push new pairs , continuing , have following error

severity    code    description project file    line    suppression state error   c2678   binary '==': no operator found takes left-hand operand of type 'std::pair<int,int>' (or there no acceptable conversion)  kurskal_algorithm   c:\program files (x86)\microsoft visual studio\2017\enterprise\vc\tools\msvc\14.10.25017\include\xutility   3161     

what wrong ? in advance

the problem in line:

if (find(b.begin(), b.end(), m.first) != b.end() && find(b.begin(), b.end(), m.second) != b.end()) 

let's check arguments of std::find call: b.begin() , b.end() std::vector<std::pair<int, int>>::iterators while m.first int.

so, you're trying find int in vector of pairs. can't that.

also, of functions lack required return statements.