foo.cc: In function 'int main()':
foo.cc:7:12: warning: unused variable 'l' [-Wunused-variable]
     uint n,l,r,mid,len=1;scanf("%u",M);for(n=1;scanf(",%u",M+n)==1;n++);*Ans=M[n-1];
            ^
foo.cc:7:14: warning: unused variable 'r' [-Wunused-variable]
     uint n,l,r,mid,len=1;scanf("%u",M);for(n=1;scanf(",%u",M+n)==1;n++);*Ans=M[n-1];
              ^
foo.cc:7:16: warning: unused variable 'mid' [-Wunused-variable]
     uint n,l,r,mid,len=1;scanf("%u",M);for(n=1;scanf(",%u",M+n)==1;n++);*Ans=M[n-1];
                ^~~
foo.cc:7:31: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     uint n,l,r,mid,len=1;scanf("%u",M);for(n=1;scanf(",%u",M+n)==1;n++);*Ans=M[n-1];
                          ~~~~~^~~~~~~~

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

{"receive":"2020-08-06T03:19:28.555Z","handle":"2020-08-06T03:19:28.555Z","cache_start":"2020-08-06T03:19:28.562Z","read_cases":"2020-08-06T03:19:28.664Z","judge":"2020-08-06T03:19:28.665Z","done":"2020-08-06T03:19:28.839Z"}