foo.cc: In function 'int main()':
foo.cc:6:15: warning: array subscript has type 'char' [-Wchar-subscripts]
    6 |  while(cin>>a[++len])
      |               ^~~~~
foo.cc:7:15: warning: array subscript has type 'char' [-Wchar-subscripts]
    7 |  if(isupper(a[len]))a[len]=tolower(a[len]);
      |               ^~~
foo.cc:7:23: warning: array subscript has type 'char' [-Wchar-subscripts]
    7 |  if(isupper(a[len]))a[len]=tolower(a[len]);
      |                       ^~~
foo.cc:7:38: warning: array subscript has type 'char' [-Wchar-subscripts]
    7 |  if(isupper(a[len]))a[len]=tolower(a[len]);
      |                                      ^~~

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