left of '.expression' must have class/struct/union - c++

Question

In this code I have an object that contains two variables hours and minutes. Im trying to consecutively add a value of 15 minutes and a value of 20 minutes to an object called t1. But I get the error : left of '.plus' must have class/struct/union.
Thanks in advance.
#include <iostream>
#include <iomanip>
using namespace std;
class Time {
public:
Time(int u, int m);
Time(int g);
void plus(Time t);
void plus(int x);
void print();
private:
int min;
int hour;
};
void Time::plus(Time t) {
min += t.min;
if (min > 59) {
hour++;
min = min - 60;
}
}
void Time::plus(int x) {
min += x;
if (min > 59) {
hour++;
min = min - 60;
}
}
void Time::print() {
cout << setw(2) << hour << " hour and " << min << " minutes";
}
Time::Time(int u, int m) : hour(u), min(m) {
}
Time::Time(int m) : hour(0), min(m) {
}
int main() {
Time t1(1, 10);
const Time kw(15);
t1.plus(kw).plus(20);
cout << "t1 = "; t1.print(); cout << endl;
cin.get();
return 0;
}

Answer 1

Right now, your plus returns void, or nothing! So you can't do t1.plus(kw).plus(20);. If you want to, you need to have your .plus() return a Time:
class Time {
public:
Time &plus(Time t);
Time &plus(int x);
...
};
I've gone ahead and made it return a Time by reference so that when you chain the function like you are, the next plus will still modify the original object the first plus was called on! We can do this if you implement the plus functions like:
Time &Time::plus(Time t) {
min += t.min;
if (min > 59) {
hour++;
min = min - 60;
}
return *this; //return ourselves so that the next func will be called on us too!
}
Time &Time::plus(int x) {
min += x;
if (min > 59) {
hour++;
min = min - 60;
}
return *this; //return ourselves so that the next func will be called on us too!
}