The program stops when it has a space input. Even when using the cin.getline

Question

so the program tells me to scan for a whitespace input. The program stops whenever the website inputs a whitespace and then immediately says that the input is not a whitespace.

#include <iostream>
#include <string>

using namespace std;

bool isWhiteSpace(char letter[0]);

int main() 
{
  char character[0];
  cout << "Enter a character: ";
  cin.getline(character,sizeof(character); 
  if(isWhiteSpace(character))
    cout << "The character you entered is a whitespace character" << endl;
  else
    cout << "The character you entered is not a whitespace character" << endl;
}

bool isWhiteSpace(char letter[0])
{
  return(isspace(letter[0])||letter[0]=='\0'||letter[0]==' ');
}

(The code has been edited but it still doesnt work)