foo.cc:3:1: warning: ISO C++ forbids declaration of ‘main’ with no type [-Wreturn-type]
    3 | main()
      | ^~~~
foo.cc: In function ‘int main()’:
foo.cc:4:15: warning: unused variable ‘y’ [-Wunused-variable]
    4 | {       int n,y,a;
      |               ^
foo.cc:11:18: warning: ‘b’ may be used uninitialized [-Wmaybe-uninitialized]
   11 |                 b++;
      |                 ~^~
foo.cc:5:16: note: ‘b’ was declared here
    5 |         double b,c,d,e;
      |                ^
foo.cc:13:18: warning: ‘c’ may be used uninitialized [-Wmaybe-uninitialized]
   13 |                 c++;
      |                 ~^~
foo.cc:5:18: note: ‘c’ was declared here
    5 |         double b,c,d,e;
      |                  ^
foo.cc:15:18: warning: ‘d’ may be used uninitialized [-Wmaybe-uninitialized]
   15 |                 d++;
      |                 ~^~
foo.cc:5:20: note: ‘d’ was declared here
    5 |         double b,c,d,e;
      |                    ^
foo.cc:17:18: warning: ‘e’ may be used uninitialized [-Wmaybe-uninitialized]
   17 |                 e++;
      |                 ~^~
foo.cc:5:22: note: ‘e’ was declared here
    5 |         double b,c,d,e;
      |                      ^