Compilare: main.cpp: In function 'int main()': main.cpp:15:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i = 0; i < S.size(); i++) letters[ S[i] ].insert(i + 1); ~~^~~~~~~~~~ main.cpp:15:50: warning: array subscript has type 'char' [-Wchar-subscripts] for(i = 0; i < S.size(); i++) letters[ S[i] ].insert(i + 1); ^ main.cpp:24:24: warning: array subscript has type 'char' [-Wchar-subscripts] letters[ S[x-1] ].erase(x); ^ main.cpp:27:24: warning: array subscript has type 'char' [-Wchar-subscripts] letters[ S[x-1] ].insert(x); ^ main.cpp:11:16: warning: unused variable 'y' [-Wunused-variable] int i, x, y, l, r, op; ^