foo.cc: In function 'int main()':
foo.cc:7:3: warning: statement has no effect [-Wunused-value]
  a>=0;
  ~^~~
foo.cc:8:3: warning: statement has no effect [-Wunused-value]
  b>=0;
  ~^~~
foo.cc:9:3: warning: statement has no effect [-Wunused-value]
  c>=0;
  ~^~~
foo.cc:10:7: warning: statement has no effect [-Wunused-value]
  a+b+c<=20;
  ~~~~~^~~~

[Hydro](https://hydro.ac)提供评测服务