/in/foo.cc: In function 'int read()':
/in/foo.cc:8:17: warning: 'ch' is used uninitialized in this function [-Wuninitialized]
  while (!isdigit(ch)) {
          ~~~~~~~^~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:7:7: warning: 'ch' may be used uninitialized in this function [-Wmaybe-uninitialized]
  char ch;
       ^~
/in/foo.cc:8:17: warning: 'ch' may be used uninitialized in this function [-Wmaybe-uninitialized]
  while (!isdigit(ch)) {
          ~~~~~~~^~~~
/in/foo.cc:7:7: note: 'ch' was declared here
  char ch;
       ^~