Removing duplicates from an unsorted array using set approach

Question

So the problem states that I have to input an array of unsorted elements containing duplicates and I decided to use sort. I am new to this and I don't understand the error

I'm trying to run it on GFG's IDE.

#include <iostream>
#include <bits/stdc++.h>

int main() {
    //code
    int n,size,a;
    cin>>n;
    while(n--)
    {
        cin>>size;
        int a[size];
        set<int> s;
        for(int i=0;i<size;i++)
          {
              cin>>a;
              s.insert(a);
          }
          for(int i=s.begin();i!=s.end();i++)
            cout<<i<<" ";
    return 0;
}

Error message:

no match for 'operator>>' (operand types are 'std::istream {aka std::basic_istream<char>}' and 'int [size]')
            cin>>a;

Why do you need an array of numbers? Make `a` to be simple `int` and your problem will be solved. — Yksisarvinen, Jul 27 '19 at 20:35
cannot convert 'std::set::iterator {aka std::_Rb_tree_const_iterator}' to 'int' in initialization for(int i=s.begin();i!=s.end();i++) -This is the new error — Tanuja RS, Jul 27 '19 at 20:38
It looks like you need [a good C++ book](https://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list). `begin()` return an *iterator* not an `int`. — Yksisarvinen, Jul 27 '19 at 20:40
Unrelated to the source of your problem, but please also see [Why should I not #include ?](https://stackoverflow.com/questions/31816095/why-should-i-not-include-bits-stdc-h) and [Why is “using namespace std;” considered bad practice?](https://stackoverflow.com/questions/1452721/why-is-using-namespace-std-considered-bad-practice) — Yksisarvinen, Jul 27 '19 at 20:41
Now that we've established that you are including ``, let's explain [why that isn't always a good idea](https://stackoverflow.com/questions/31816095/why-should-i-not-include-bits-stdc-h) — , Jul 27 '19 at 20:41
I shall read up o iterators. Yes. Thank you for your inputs. I actually do not understand how begin() works — Tanuja RS, Jul 27 '19 at 20:43

score 1 · Answer 1 · 2019-07-27T20:56:31.863

The source of the error you show is this line right here:

int main() {
   //...
       int a[size]; 
   // ...
}

a is an array now, which has no operator>>() overloaded for it for std::istream.

The solution is simple, just change this line:

cin>>a;

to this:

cin>>a[i];

Now, there should be no compiling problems, although a ton of bad practices still, which several answers and other comments and an answer has attempted to correct. I'll leave that to them.

The only thing I will warn you about is

int a;
some block {
   int a[size];
}
// try to use a:
a[i]; // bad

There are 2 variables named a in your program. Once the second a goes out of scope, it will destroy the array version of a, and use the regular int a instead. Just be wary of this.

P.S. Okay, so I will mention another one that seems unmentioned by others.

The following is ill formed, since it tries to use a variable-length array:

cin>>size;
int a[size];

Some compilers will support it, but technically, that is an ill-formed program. As a general rule, don't do it.

Thank you :) I shall do the needful – Tanuja RS Jul 27 '19 at 20:55 — Tanuja RS, Jul 27 '19 at 20:55

Removing duplicates from an unsorted array using set approach

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