Question

In the code above the else-if part gives me error. The meaning of else-if is: else if the value of x isn’t in the deque then…

#include <iostream>
#include <ctime>
#include <stack>
#include <deque>
#include <algorithm>
deque<char> visited;
char x;

   if (x==target[4][4])
   {
           visited.push_back(x);            
           return (visited);
   }
   else if (!(find(visited.begin(), visited.end(), x)))
   {
       visited.push_back(x);
   }

ERROR:no operator “!” matches these operands

Answer 1

If std::find cannot find the specific value, it will return the “end” of the iterator pair.

else if (std::find(visited.begin(), visited.end(), x) == visited.end())
{
   // process the case where 'x' _is_not_ found between
   // visited.begin() and visited.end()

---

Edit: If you want to know if x is in the deque, just reverse the condition.

else if (std::find(visited.begin(), visited.end(), x) != visited.end())
{
   // process the case where 'x' _is_ found between
   // visited.begin() and visited.end()

---

Edit: If you are unfamiliar with the iterator concept in C++, please read Understanding Iterators in the STL.