foo.cc: In function 'int main()':
foo.cc:7:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%f,%f,%c",&a,&b,&c);
  ~~~~~^~~~~~~~~~~~~~~~~~~~~
foo.cc:23:8: warning: 's' may be used uninitialized in this function [-Wmaybe-uninitialized]
  printf("%.2f",s); 
  ~~~~~~^~~~~~~~~~

[Hydro](https://hydro.ac)提供评测服务