foo.cc: In constructor ‘BigInt::BigInt()’:
foo.cc:7:5: warning: ‘BigInt::x’ is initialized with itself [-Winit-self]
    7 |     BigInt():x(x)
      |     ^~~~~~
foo.cc: In function ‘int main()’:
foo.cc:49:9: warning: unused variable ‘x’ [-Wunused-variable]
   49 |     int x, k;
      |         ^
foo.cc:49:12: warning: unused variable ‘k’ [-Wunused-variable]
   49 |     int x, k;
      |            ^
foo.cc: In constructor ‘BigInt::BigInt()’:
foo.cc:7:16: warning: ‘*this.BigInt::x’ is used uninitialized [-Wuninitialized]
    7 |     BigInt():x(x)
      |                ^