Compilare: main.cpp: In function 'bool f1()': main.cpp:43:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while ((i + 3) < s.size() && s.substr(i, 4) == " OR ") { ~~~~~~~~^~~~~~~~~~ main.cpp: In function 'bool f2()': main.cpp:52:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while ((i + 4) < s.size() && s.substr(i, 5) == " AND ") { ~~~~~~~~^~~~~~~~~~ main.cpp: In function 'bool f3()': main.cpp:61:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if ((i + 3) < s.size() && s.substr(i, 4) == "NOT ") { ~~~~~~~~^~~~~~~~~~ main.cpp: In function 'bool f4()': main.cpp:80:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] else if ((i + 3) < s.size() && s.substr(i, 4) == "TRUE") { ~~~~~~~~^~~~~~~~~~ main.cpp:84:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] else if ((i + 4) < s.size() && s.substr(i, 5) == "FALSE") { ~~~~~~~~^~~~~~~~~~ main.cpp:89:23: warning: array subscript has type 'char' [-Wchar-subscripts] ans = val[s[i]]; ^ main.cpp: In function 'int main()': main.cpp:104:14: warning: array subscript has type 'char' [-Wchar-subscripts] val[c] = !val[c]; ^ main.cpp:104:24: warning: array subscript has type 'char' [-Wchar-subscripts] val[c] = !val[c]; ^