Why am I getting an error here? (C++/C)

Question

Code:

#include <iostream>
#include <fstream>
#include <cstring>

using std::cout;
using std::endl;

int main() {

std::fstream fileIO;
fileIO.open("out.txt", std::ios::app);

if (fileIO.is_open()) {
char* str;
scanf("%s", str);
while (strcmp(str, "") != 0) {
fileIO << str << "\n";
scanf("%s", str);
}
} else
cout << "Couldn't open file :(" << endl;

fileIO.close();

return 0;
}

Answer 1

where are you running that code?
pointer str is passed to scanf without initializing it . it has to point to some location on memory for scanf to store data there.

Answer 2

Bahha🐧 I'm running that code on Repl.it.
Thanks for the answer, I understand now that I need to either allocate on the heap via malloc/new or type: char str[some bytes].