foo.cc: In function 'int D(int)':
foo.cc:12:26: warning: unused variable 'b' [-Wunused-variable]
  int x;int x1;int x3;int b;
                          ^
foo.cc: In function 'int main()':
foo.cc:6:13: warning: 'x2' is used uninitialized in this function [-Wuninitialized]
  int x2=D(x2);
             ^