I have to redo programming exercise 5 of chapter 9 using dynamic arrays. but I have the information but I don't know how to use it in a dynamic arrays please help.

Question

//Chapter 9: Programming Exercise 5

#include <iostream>
#include <cstring>
#include <cctype>

using namespace std;

int main()
{
char str[81];

int len;

int i;

cout << "Enter a string: ";
cin.get(str, 80);
cout << endl;
cout << "String in upper case letters is:" << endl;

len = strlen(str);
for (i = 0; i < len; i++)
cout << static_cast<char>(toupper(str[i]));
cout << endl;

return 0;
}