foo.cc: In function 'float sum(float, float, char)':
foo.cc:15:10: warning: control reaches end of non-void function [-Wreturn-type]
   15 |    cout<<"输入错误";
      |          ^~~~~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:23:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   23 |  scanf("%f,%f,%c",&a,&b,&c);
      |  ~~~~~^~~~~~~~~~~~~~~~~~~~~

[Hydro](https://hydro.ac)提供评测服务