/in/foo.cc: In function 'Data calc()':
/in/foo.cc:52:30: warning: array subscript has type 'char' [-Wchar-subscripts]
    while (n1 > 0 && id[s1[n1]] <= id[c]) {
                              ^
/in/foo.cc:52:39: warning: array subscript has type 'char' [-Wchar-subscripts]
    while (n1 > 0 && id[s1[n1]] <= id[c]) {
                                       ^
/in/foo.cc: In function 'int compute(int, int, char)':
/in/foo.cc:31:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^