foo.cc: In function 'int main()':
foo.cc:33:6: warning: variable 'a' set but not used [-Wunused-but-set-variable]
  int a,b,c,i,n1,n2;
      ^
foo.cc:33:8: warning: variable 'b' set but not used [-Wunused-but-set-variable]
  int a,b,c,i,n1,n2;
        ^
foo.cc:33:10: warning: unused variable 'c' [-Wunused-variable]
  int a,b,c,i,n1,n2;
          ^
foo.cc:33:12: warning: unused variable 'i' [-Wunused-variable]
  int a,b,c,i,n1,n2;
            ^

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。