fix: Add c++ suggested code

dynamic_programming/fibonacci_top_down.cpp

@@ -5,24 +5,24 @@
  * deliberately used size_t to increase the calculation of fibb series.
  * Now calculates upto 93 fibbonacci terms.
  */
+#include <array>
 #include <iostream>
-using namespace std;
-
-size_t arr[1000000] = {0, 1};
+std::array<size_t, 1000000> arr = {0, 1};
 
 size_t fib(int n) {
- if (n <= 1)
+ if (n <= 1) {
  return arr[n];
+ }
  if (!arr[n]) {
  arr[n] = fib(n - 1) + fib(n - 2);
  }
  return arr[n];
 }
 
 int main(int argc, char const *argv[]) {
- int n;
- cout << "Enter n: ";
- cin >> n;
- cout << "Fibonacci number is " << fib(n) << endl;
+ int n = 0;
+ std::cout << "Enter n: ";
+ std::cin >> n;
+ std::cout << "Fibonacci number is " << fib(n) << std::endl;
  return 0;
 }