Compilare: main.cpp: In function 'int main()': main.cpp:16:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i<a.size(); ++i) ~^~~~~~~~~ main.cpp:31:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = start; i<a.size(); ++i) ~^~~~~~~~~ main.cpp:34:20: warning: array subscript has type 'char' [-Wchar-subscripts] fr[a[i]]++,lit++; ^ main.cpp:36:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = start; i<a.size(); ++i) ~^~~~~~~~~ main.cpp:40:33: warning: array subscript has type 'char' [-Wchar-subscripts] v[i] = lit - fr[a[i]]; ^ main.cpp:41:20: warning: array subscript has type 'char' [-Wchar-subscripts] fr[a[i]]--,lit--; ^ main.cpp:44:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = start; i<a.size(); ++i) ~^~~~~~~~~ main.cpp:49:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(i < a.size()) ~~^~~~~~~~~~ main.cpp:57:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(i < a.size() && a[i] >= 'a' && a[i] <= 'z') ~~^~~~~~~~~~