/in/foo.c: In function 'main':
/in/foo.c:8:3: warning: statement with no effect [-Wunused-value]
  v==PI*r*r*h;
  ~^~~~~~~~~~
/in/foo.c:8:11: warning: 'h' is used uninitialized in this function [-Wuninitialized]
  v==PI*r*r*h;
     ~~~~~~^~
/in/foo.c:9:2: warning: 'v' is used uninitialized in this function [-Wuninitialized]
  printf("%.2f",v);
  ^~~~~~~~~~~~~~~~