count

#include <bits/stdc++.h> 
using namespace std; 
int main() 
{ 
    int arr[] = { 14, 12, 15, 11, 10 }; 
    // initializes the set from an array 
    set<int> s(arr, arr + 5); 
    // check if 11 is present or not 
    if (s.count(11)) 
        cout << "11 is present in the set\n"; 
    else
        cout << "11 is not present in the set\n"; 
    // checks if 18 is present or not 
    if (s.count(18)) 
        cout << "18 is present in the set\n"; 
    else
        cout << "18 is not present in the set\n"; 
    return 0; 
}

输出：
11 is present in the set
18 is not present in the set