Why is the array filled with the letter H?

Question

C++ / C#

#include <iostream>;
#include <conio.h>;
#include <ctime>;

using namespace std;


int main() {
  setlocale(0, "");
  
  char **arr = new char*[10];

  for (int i = 0; i < 10; i++) {
    arr[i] = new char[10];
  }

  arr[0][1] = 'K';
  arr[0][2] = 'L';

  for (int i = 0; i < 10; i++) {
    for (int z = 0; z < 10; z++) {
      cout << arr[i][z] << endl;
    }
  }

  system("pause");
  return 0;
}

Answer 1

The memory is not initialized, so there is garbage. What exactly is Unspecified Behavior.

Answer 2

In general, this is rather strange, no unspecified behavior should occur, since the new expression calls the default constructor for each object, that is, built-in types must be initialized to zero .
Try to display not a symbol, but its code, replacing one line with:
Secondly, endl not only translates to a new line, but also resets the accumulated buffer, that is, immediately displays everything on the screen or in a file. If you have a lot of output, this can seriously slow down your program. For a simple newline, output a special control character'\n'
If you output a matrix (two-dimensional array), it is more convenient to do it like this:

for (int i = 0; i < 10; i++) {
    for (int j = 0; j < 10; j++) {
        cout << arr[i][j] << ' '; // пробел можно убрать
    }
    cout << '\n';
}

Also, you should never use the system. It pauses your program and starts another one (in this case pause). This option is not only not optimal, but also platform-dependent. People who use mac or linux will have to make changes to your code in order to run it, since these OSes do not have the pause. Use the C++ language tools for this: cin.get();
And never use the conio.h header file again . It is not part of the C or C++ language standard, and is not supported by most compilers.
PPS What compiler are you using? What version is it? What are the compilation keys or project settings in the IDE?