returning reference of a class - c++

Question

well i have a bit problem understanding references in c++, especially while returning reference of a class from a method.
like the code below works perfectly:(the bold portion is where the problem lies)
#include<iostream>
using namespace std;
class Sequence
{
int *a;
int length;
void allocMemory()
{
this->a = new int[this->length];
}
void fill(int val)
{
for (int i = 0; i<this->length; i++) this->a[i] = val;
}
public:
Sequence(int len=0)
{
this->length=len;
this->allocMemory();
this->fill(0);
}
Sequence(int data,int len)
{
this->length=len;
this->allocMemory();
this->fill(data);
}
Sequence(int *data,int len)
{
this->length=len;
this->allocMemory();
for(int i=0;i<this->length;i++) this->a[i]=data[i];
}
Sequence(const Sequence &s)
{
length=s.length;
allocMemory();
for(int i=0;i<length;i++){
a[i]=s.a[i];
}
}
~Sequence()
{
delete [] this->a;
}
friend ostream & operator<<(ostream &stream, Sequence &s)
{
stream << "Sequence: " ;
for(int i=0;i<s.length;i++) stream << s.a[i] << " ";
stream << " Length = " << s.length << endl;
return stream;
}
friend istream & operator>>(istream &stream, Sequence &s)
{
int n;
cout << "No of elements:";
stream >> n;
s.length=n;
s.allocMemory();
cout << "Enter the elements:";
for(int i=0;i<n;i++) stream >> s.a[i];
return stream;
}
Sequence &operator= (int data){ // this method works fine as i return a reference
for(int i=0;i<length;i++){
a[i]=data;
}
return *this;
}
**Sequence operator+(Sequence ob){
/*this is the problematic method. It works fine this way. as i already got
the necessary copy constructor code. But if i change the return value to a
reference like the sample code within the comment, the program doesn't give the correct output. Though as per my theoretical knowledge, i can't find any problem in this code which too should run perfectly even if the copy constructor code was missing.
Sequence & operator+(Sequence ob){
int i,j;
int l=length+ob.length;
Sequence temp(0,l);
for(i=0;i<length;i++){
temp.a[i]=a[i];
}
for(j=0;i<l || j<ob.length;i++,j++){
temp.a[i]=ob.a[j];
}
return temp;
}
*/**
int i,j;
int l=length+ob.length;
Sequence temp(0,l);
for(i=0;i<length;i++){
temp.a[i]=a[i];
}
for(j=0;i<l || j<ob.length;i++,j++){
temp.a[i]=ob.a[j];
}
return temp;
}
void show(){
for(int i=0;i<length;i++){
cout<<a[i]<<" ";
}
}
};
int main(){
int arr[]={1,2,3,4,5,6,7,8,9,10};
Sequence a(arr,10);
cout << a;
Sequence b(10);
cout << b;
cin >> b;
cout << b;
Sequence c=a+b;
c.show();
}

Answer 1

You can't return a temporary by reference - you'd be left with a dangling reference outside the function because the object is destroyed when the function ends.
Idiomatically, operator+ returns by value. In comparison, operator+= returns by reference (to enable chaining), but you'd return *this, which isn't temporary and makes it valid.