# list and vector iterator [fltk]

Bjarne Stroustrup “Programming Principles and Practice Using C++”
Chapter 14 Exercise 15
Using GUI library called FLTK (Fast Light Tool Kit, “full tick”).

[code language=”cpp”]
// Philipp Siedler
// Bjarne Stroustrup’s PP
// Chapter 14 Exercise 15

#include "std_lib_facilities.h"

class Base_iterator
{
public:
virtual double* next() = 0;
protected:
int count;
};

//————————VECTOR ITERATOR

class Vector_iterator : public Base_iterator
{
public:
Vector_iterator(vector<double>& v);
double* next();
private:
vector<double> vec;
};

Vector_iterator::Vector_iterator(vector<double>& v)
{
vec = v;
count = 0;
}

double* Vector_iterator::next()
{
if (vec.size() > 0 && count < vec.size()) {

count++;
return &vec[count – 1];
}
else {
return 0;
}
}

//————————LIST ITERATOR

class List_iterator : public Base_iterator
{
public:
List_iterator(list<double>& l);
double* next();
private:
list<double> lis;
list<double>::iterator pointer;
};

List_iterator::List_iterator(list<double>& l)
{
lis = l;
pointer = lis.begin();
}

double* List_iterator::next() {
double* p;

if (lis.size() && lis.size() > distance(lis.begin(), pointer)) {
p = &*pointer;
pointer++;
return p;
}
else return 0;
}

void print(Base_iterator& iterator)
{
double* pointer;
pointer = iterator.next();

while (pointer != 0) {
cout << *pointer << endl;
pointer = iterator.next();
}
}

int main()
try
{
vector<double> v;
v.push_back(2.0);
v.push_back(2.1);
v.push_back(2.2);
v.push_back(2.3);

list<double> l;
l.push_back(2.0);
l.push_back(2.1);
l.push_back(2.2);
l.push_back(2.3);

Vector_iterator vi(v);
print(vi);

List_iterator li(l);
print(li);

keep_window_open();
}
catch (exception& e) {
cout << e.what() << endl;
return 1;
}
catch (…) {
cout << "Exiting" << endl;
return 2;
}
[/code]

```Output:
2
2.1
2.2
2.3
2
2.1
2.2
2.3
Please enter a character to exit
```