/in/foo.cc: In function 'int main()':
/in/foo.cc:17:13: warning: unused variable 'equ' [-Wunused-variable]
     char op,equ;
             ^~~
/in/foo.cc:22:29: warning: 'tag4' may be used uninitialized in this function [-Wmaybe-uninitialized]
         int tag1 ,tag2,tag3,tag4,tag5;
                             ^~~~
/in/foo.cc:22:24: warning: 'tag3' may be used uninitialized in this function [-Wmaybe-uninitialized]
         int tag1 ,tag2,tag3,tag4,tag5;
                        ^~~~
/in/foo.cc:22:19: warning: 'tag2' may be used uninitialized in this function [-Wmaybe-uninitialized]
         int tag1 ,tag2,tag3,tag4,tag5;
                   ^~~~
/in/foo.cc:49:13: warning: 'op' may be used uninitialized in this function [-Wmaybe-uninitialized]
             if(op == '+') ans = c - b;
             ^~