What is the C++ equivalent for Python...

Hi everyone

In Python, I know how the following works:

Code:

>>> SET = []
>>> SET.append(1)
>>> print SET
[1]

An empty set is first defined.
The integer 1 is added/appended to the set.
The set is printed, having one new element instead of being empty.

How would I go about doing this in C++?
Would it look something like this?

Code:

#include <iostream>
#include <set>
using namespace std;

int main()
{
    set<int> SET;
    SET.insert(1)
    cout << SET << endl;
}

I tried doing that but I got an error saying
no match for 'operator<<' in 'std::cout << SET'
I am using DevC++ 4.9.9.2 and Python 2.7

Thank you all in advance

You'll have to walk the set and print each member.

How can I append new elements to the set as shown in the Python example?
Is there a way to declare an empty set and add new members to it?

Unfortunately, you cannot print a std::set using operator<<. You do have a few options, e.g., manually write a loop to do it, or use a generic algorithm.

By the way, I believe that the Python code defines a list, not a set. This would be more akin to a sequential container in C++ like an array, or std::vector, or std::list.

Despite the fact that you're calling that variable SET, it is not a set. It's a list. The appropriate C++ container would be std::vector<> not std::set<>.

(Python "lists" are actually arrays.)

EDIT: Doof. Laserlight already pointed that out.

You could also overload an operator << for a set, or vector or whatever. Then you could call cout << my_set;
There is no predefined, but make it once, use it always.

Thanks guys.

I'm still quite confused >_<

I went ahead and looked up std::list at
Cprogramming.com - STL Tutorial - List Container

I copied and pasted the last portion:

Code:

std::list<int> int_list;
int_list.push_back(1);
int_list.push_back(1);
int_list.push_back(8);
int_list.push_back(9);
int_list.push_back(7);
int_list.push_back(8);
int_list.push_back(2);
int_list.push_back(3);
int_list.push_back(3);
int_list.sort();
int_list.unique();

for(std::list<int>::iterator list_iter = int_list.begin(); 
    list_iter != int_list.end(); list_iter++)
{
    std::cout<<list_iter<<endl;
}

I have the same error as before (which is strange since I thought this would be a working model).
I don't know all the terms being used in your answers.

If it doesn't bother you guys, could you post the simplest sample code that would reflect the behaviour of defining a list/set/array and inserting elements to it?
I understand that those datatypes slightly differ, but I'll look into those right now.
I'm taking notes as I go, but things are a bit confusing still.

Thanks for all your help. Much appreciated!

Originally Posted by CPlus

Thanks guys.

I'm still quite confused >_<

I went ahead and looked up std::list at
Cprogramming.com - STL Tutorial - List Container

I copied and pasted the last portion:

Code:

std::list<int> int_list;
int_list.push_back(1);
int_list.push_back(1);
int_list.push_back(8);
int_list.push_back(9);
int_list.push_back(7);
int_list.push_back(8);
int_list.push_back(2);
int_list.push_back(3);
int_list.push_back(3);
int_list.sort();
int_list.unique();

for(std::list<int>::iterator list_iter = int_list.begin(); 
    list_iter != int_list.end(); list_iter++)
{
    std::cout<<list_iter<<endl;
}

I have the same error as before (which is strange since I thought this would be a working model).
I don't know all the terms being used in your answers.

If it doesn't bother you guys, could you post the simplest sample code that would reflect the behaviour of defining a list/set/array and inserting elements to it?
I understand that those datatypes slightly differ, but I'll look into those right now.
I'm taking notes as I go, but things are a bit confusing still.

Thanks for all your help. Much appreciated!

You need this:

Code:

std::cout<<*list_iter<<endl;

list_iter itself is not an object, it merely points to where the object is. You have to follow that pointer to find the object.

Originally Posted by tabstop

You need this:

Code:

std::cout<<*list_iter<<endl;

list_iter itself is not an object, it merely points to where the object is. You have to follow that pointer to find the object.

* here is the dereference operator. When used in a declaration(eg, "char *ptr"), the asterisk indicates a pointer to a type.

I think python uses references but not pointers, so the concept of pointers and dereferencing may be something new.

Thanks! That worked.

If int_list is the list, is there any way I can cout the Nth element in it?
For example, if int_list was 1,1,2,6,24,120
then
int_list[0] would be 1,
int_list[1] would be 1,
int_list[2] would be 2,
int_list[3] would be 6,
int_list[4] would be 24,
int_list[5] would be 120,

Thanks in advance
You guys are a lot of help.

For that you should use std::vector which allows random access.

Most containers overload the index operator, so the syntax you listed should work.

Originally Posted by CPlus

If int_list is the list, is there any way I can cout the Nth element in it?

Not with a list. With a vector, a deque, or a C array you can use [], eg:

Code:

vector<int> myray;
[...]
cout << myray[n];

vector is actually your basic dynamic array most akin to whatever it is called in python (set or list; dunno why they didn't just call it an array). A deque may be more exactly so; a C++ STL list is actually less like an array than either the vector or the deque.

You don't have random access for a list. But you can do the walking algorithm that you just did, but with a counter to tell you when to stop.

It works

The code I used was:

Code:

int main()
{
    vector<int> VECTOR;
    VECTOR.push_back(1);
    VECTOR.push_back(1);
    VECTOR.push_back(2);
    VECTOR.push_back(6);
    VECTOR.push_back(24);    
    cout << VECTOR[4] << endl;
}

Which outputted 24.


I have another question that is related to all of this.
In Python, a user can input a list, such as:

Code:

LIST = input("Input your list here: ")
LIST.append(1)
print LIST

What this does is ask the user to input a list called LIST.
Afterward, LIST has the number 1 appended to it.
If the user writes [0,1,2,3,4,5] as their input LIST, the
script outputs [0,1,2,3,4,5,1]

Would the C++ equivalent look something like this?

Code:

int main()
{
    // VECTOR defined here
    vector<int> VECTOR;

    // User inputs into VECTOR
    std::cin>>VECTOR;

    // Adds "1" into VECTOR
    VECTOR.push_back(1);

    // couts from 0 to Vector size
    for (i==0;i<(VECTOR.size());i++)
    {
        cout << VECTOR[i] << endl;
    }
}

Thanks for all your help