Isn’t the value of an unassigned int variable in C++ 0 (zero)?

Question

I’m having my first serious contact with C++.

I wanted to see what would happen if I added up a value int of a variable assigned with another without assigning, and see what happened:

#include <cstdio>

using namespace std;


int main()
{

    int num;
    int num2; // Não atribuido

    num = 10;

    printf("O valor é %d\n", num + num2);

    return 0;
}

The result obtained was:

The value is 134513787

I’m not criticizing the language, but I wanted to understand why the printed value was this, rather than printing "The value is 10", since num2 has no integer assigned.

Is there any explanation why the returned value is this?