Compilare: user.cpp: In function ‘int cst(int, int)’: user.cpp:23:14: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(st < s.size()) { ^ user.cpp:24:36: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j=0; j < k && st+j < s.size(); j++) { ^ user.cpp:25:22: warning: array subscript has type ‘char’ [-Wchar-subscripts] f[s[st+j]] ++; ^ user.cpp:26:24: warning: array subscript has type ‘char’ [-Wchar-subscripts] nel[s[st+j]] += (f[s[st+j]] > 1); ^ user.cpp:26:39: warning: array subscript has type ‘char’ [-Wchar-subscripts] nel[s[st+j]] += (f[s[st+j]] > 1); ^ user.cpp:28:36: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j=0; j < k && st+j < s.size(); j++) { ^ user.cpp:29:22: warning: array subscript has type ‘char’ [-Wchar-subscripts] f[s[st+j]] --; ^ user.cpp:35:17: warning: array subscript has type ‘char’ [-Wchar-subscripts] if(lua[z] > 0) { ^ user.cpp:36:32: warning: array subscript has type ‘char’ [-Wchar-subscripts] ch.push_back({lua[z], {0, z}}); ^ user.cpp:37:32: warning: array subscript has type ‘char’ [-Wchar-subscripts] ch.push_back({nel[z], {1, z}}); ^ In file included from /usr/include/c++/5/cassert:43:0, from user.cpp:6: user.cpp:38:25: warning: array subscript has type ‘char’ [-Wchar-subscripts] assert(lua[z] != nel[z]); ^ user.cpp:38:35: warning: array subscript has type ‘char’ [-Wchar-subscripts] assert(lua[z] != nel[z]); ^ user.cpp:40:12: warning: array subscript has type ‘char’ [-Wchar-subscripts] f[z] = nel[z] = used[z] = 0; ^ user.cpp:40:21: warning: array subscript has type ‘char’ [-Wchar-subscripts] f[z] = nel[z] = used[z] = 0; ^ user.cpp:40:31: warning: array subscript has type ‘char’ [-Wchar-subscripts] f[z] = nel[z] = used[z] = 0; ^ user.cpp: In function ‘int main()’: user.cpp:66:14: warning: array subscript has type ‘char’ [-Wchar-subscripts]