create

1. insert

set<T> s;
s.insert(val);

#include <iostream>
#include <set>
using namespace std;
int main() {
    set<int> s;
    s.insert(5);
    s.insert(1);
    s.insert(90);
    int a[] = {7, 8, 9};
    s.insert(a, a + sizeof(a)/sizeof(int));
    for (auto it = s.begin(); it != s.end(); it++) {
        cout << *it << endl;
    }
    return 0;
}

set will be in order automatically

retrieve

1. find

#include <iostream>
#include <set>
using namespace std;
int main()
{
    set<int> myset;
    set<int>::iterator it;

    // set some initial values:
    for (int i = 1; i <= 5; i++)
        myset.insert(i * 10); // set: 10 20 30 40 50

    it = myset.find(20);
    myset.erase(it);
    myset.erase(myset.find(40));
    // myset.erase(myset.find(60)); //wrong
    it = myset.find(60);
    if (it != myset.end())
        myset.erase(it);

    cout << "myset contains:";
    for (it = myset.begin(); it != myset.end(); ++it)
        cout << ' ' << *it;
    cout << '\n';

    return 0;
}

myset contains: 10 30 50

2.count

#include <iostream>
#include <set>
using namespace std;
int main()
{
    set<string> myset;
    set<int>::iterator it;

    myset.insert("1");
    myset.insert("1");

    cout << myset.count("1") << endl;
    cout << myset.count("2") << endl;

    return 0;
}

1
0

delete

1. erase

#include <iostream>
#include <set>
using namespace std;
int main()
{
    set<int> myset;
    set<int>::iterator it;

    // insert some values:
    for (int i = 1; i < 10; i++)
        myset.insert(i * 10);
    
    it = myset.begin();
    ++it;

    myset.erase(it); //erase by iterator

    myset.erase(40); //erase by value

    it = myset.find(60);
    myset.erase(it, myset.end()); //erase by a interval

    cout << "myset contains:";
    for (it = myset.begin(); it != myset.end(); it++)
        cout << ' ' << *it;
    cout << '\n';

    return 0;
}

myset contains: 10 30 50

#include <iostream>
#include <set>
using namespace std;
int main()
{
    set<string> myset;
    set<int>::iterator it;

    myset.insert("1");

    int i = myset.erase("2");
    cout << i << endl;
    
    int j = myset.erase("1");
    cout << j << endl;

    return 0;
}