Fibonacci Code using Dynamic Programming

Fibonacci_DP.cpp

// Online C++ compiler to run C++ program online
#include <iostream>
using namespace std;
unsigned long X[100];

bool doesExist(int n){
        
        if (X[n] != -1)
            return true;
            
    return false;
}

unsigned long fun(int n )
{       
    if (n == 0 || n== 1)
            return n;
        if ( doesExist(n) ) 
            return X[n];
            
        X[n] = fun(n-1) + fun(n-2) ;
        
        return X[n];
            
}
int main() {
  fill_n(X, 100, -1);
  
  cout << fun(99)<<"  ";    
 
    return 0;
}