Hi everybody, I have an assignment to create a grading system using multimap. It's not completed yet at the moment but whenever i try to compile it tells me "no match for 'operator[]' in lines 56,57,etc. I've scoured several help sites, and my textbook but i cant find any solutions. Can anyone help me? Thanks so much in advance! Code: #include <iostream> #include <string> #include <map> using namespace std; class Student { public: //--- Constructor Student (int id = 0, double gpa = 0); //--- Output operator friend ostream & operator<<(ostream & out, const Student & s); //--- Input operator friend istream & operator>>(istream & in, Student & s); //--- Less-than operator friend bool operator<(const Student & a, const Student & b); private: //--- Data members int myId; double myGPA; }; // end of class Student //--- Definition of constructor inline Student::Student(int id, double gpa) : myId(id), myGPA(gpa) { } //--- Definition of input operator inline istream & operator>>(istream & in, Student & s) { in >> s.myId >> s.myGPA; } //--- Definition of output operator inline ostream & operator<<(ostream & out, const Student & s) { out << "id = " << s.myId << " GPA = " << s.myGPA; return out; } //--- Definition of less-than operator inline bool operator<(const Student & a, const Student & b) { return a.myId < b.myId; } //================================================================ int main() { //typedef multimap<string, Student>grades typedef multimap< string, Student, less<string> > grades1; typedef multimap< Student, string, less<Student> > grades2; grades1 a1; // associative array of Student, index type is string grades2 a2; // associative array of string, index type is Student Student s; s = Student(12345, 3.3); a1["Fred"] = s; a2[s] = "Fred"; s = Student(32322, 3.9); a1["Al"] = s; a2[s] = "Al"; s = Student(13131, 2.5); a1["Joan"] = s; a2[s] = "Joan"; s = Student(22121, 4.0); a1["Barb"] = s; a2[s] = "Barb"; s = Student(28888, 2.9); a1["George"] = s; a2[s] = "George"; s = Student(19981, 3.0); a1["Dot"] = s; a2[s] = "Dot"; s = Student(20012, 2.9); a1["Sue"] = s; a2[s] = "Sue"; string name; cout << "Enter a name: "; cin >> name; grades1::iterator it1 = a1.find(name); cout << name << " has "; if (it1 == a1.end()) cout << "no info"; else cout << a1[name]; cout << endl; Student aStudent; cout << "Enter a Student's id and GPA: "; cin >> aStudent; grades2::iterator it2 = a2.find(aStudent); cout << "Student " << aStudent << " is "; if (it2 == a2.end()) cout << "no info"; else cout << a2[aStudent]; cout << endl; }
This error means that class multimap does not define operator[]; i.e. you cannot use the syntax you're trying to use on lines 56-62: Code: a1["Fred"] = s; If you want to do this then you'll have to define a new class derived from multimap which implements operator[]. Also you can see here that there is no definition for operator[]: http://en.cppreference.com/w/cpp/container/multimap