declare fixed size character array on stack c++

I am attempting to create a character array of a fixed size on the stack (it does need to be stack allocated). the problem I am having is I cannot get the stack to allocate more than 8 bytes to the array:

#include <iostream>
using namespace std;

int main(){
        char* str = new char[50];
        cout << sizeof(str) << endl;

        return 0;
}

prints

8

How do I allocate a fixed size array (in this case 50 bytes. but it may be any number) on the stack?