core dumped when run this simple D program.

[Fox via Digitalmars-d-learn]

import std.stdio;

class myClas_1 {
        int a;
}
void main() {
        myClas_1 c1;
        writeln(c1.a);
}


===================
what's wrong? dmd and gdc both can compile these code, but can't 
run either.
DMD64 D Compiler v2.109.1
gcc 14.2.1 20240824 (GCC)
fedora 41
thanks!