AcWing 830. monotonous stack

https://www.acwing.com/problem/content/832/

#include <iostream>
using namespace std;
const int N = 100010;
int stk[N], tt;
int main() {
    int n;
    cin >> n;
    while (n -- ) {
        int x;
        Scanf ( " % D " , & X);
         the while (TT && STK [TT]> = X) // if the stack is not empty and the stack of elements is greater than the current figure, then the stack of elements is not will be used    
        TT - ;
         IF (! TT) the printf ( " -1 " );    // if is greater than, is not described, it outputs -1 
        the else the printf ( " % D " , STK [TT]); // If there is less than, the outputs 
        STK [TT ++] = x; // then go into the x 
    }
     return  0 ;
}