getting a SIGSEGV (segmentation fault) - c++

Question

I'm creating a generic box with a template. Basically something like a queue or linked list. I keep getting a SIGSEGV for some reason and I can't figure it out. I take in an integer or a string from the user in main and then the constructor makes allocates memory for the generic box to exist, then using function inert_First (there are a lot more functions like insert_Mid, insert_last, delete_Mid etc) and it keeps telling me I'm accessing wrong memory but I don't know where ?
this is the class
template<class T>
class g_Box
{
int first,mid,last;
int no_Of_Ele;
int capacity;
T *ele;
public:
g_Box();
g_Box(int);
void insert_First(T);
};
this is the constructor
template<class T>
g_Box<T>::g_Box(){
first=-1, last=-1, mid=-1;
no_Of_Ele=0;
capacity=10;
T *ele = new T[capacity];
}
template<class T>
g_Box<T>::g_Box(int a){
first=-1, last=-1, mid=-1;
no_Of_Ele=0;
capacity=a;
T *ele = new T[capacity];
}
This is the insert_First
template<class T>
void g_Box<T>::insert_First(T a){
if(isFull()){
cout<<"The box is full";
}
else if(isEmpty()){
first=0; last=0; mid=(first+last)/2;
ele[0]=a;
no_Of_Ele++;
}
else{
T *ele2 = new T[capacity];
//T ele2[capacity];
for(int i=0; i<no_Of_Ele; i++){
ele2[i]=ele[i];
}
for(int i=0; i<no_Of_Ele; i++){
ele[i+1]=ele2[i];
}
ele[first]=a;
last++;
mid=(first+last)/2;
no_Of_Ele++;
delete[] ele2;
}
}
and this is the main
int main()
{
g_Box<int> g;
int data;
cin>>data
g.insert_First(data);
}