/in/foo.cc: In function 'int main()':
/in/foo.cc:13:12: warning: array subscript has type 'char' [-Wchar-subscripts]
   13 |    num[a[j]]++;
      |            ^
/in/foo.cc:51:27: warning: 'rec' may be used uninitialized in this function [-Wmaybe-uninitialized]
   51 |    if(lena%2!=0) sub2=sub2+rec+sub1;
      |                       ~~~~^~~~