#include <bits/stdc++.h>
using namespace std;

int main() 
{
    
    // SET

// given n elements , tell me the number of unique elements 

set<int> st;

int n;
cin>>n;

for(int i=0; i<n; i++){
  
  int x;
  cin>>x;
  
  st.insert(x);
}

int count=0;

for(auto it : st){
count++;
  
}

cout << count;

/* erase functionality

st.erase(st.begin()); // for deleting the first elements

st.erase(st.begin(), st.begin() + 2); // for deleting the 
                                    // elements in range
                                    
*/

// for deleting the particular key in set

st.erase(5); // st.erase(key);
              // delete the 5


// to find the particular element in the set
 auto it = st.find(key);

st.emplace(8);  // similar to insert 
                // but slightly faster
                
cout << st.size() // printing the size of the set


//  UNORDERED SET

unordered_set<int> st;

st.insert(2);
st.insert(3);
st.insert(4);

// average time complexity is 0(1)
// tle->switch to SET
// but the worst case is linear in nature , 0(set value)



// MULTI SET


multiset<int> ms;

ms.insert(1);
ms.insert(2);
ms.insert(3);

// all the other functions are similar 

                                    
}
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Read inputs from stdin

OneCompiler's C++ online compiler supports stdin and users can give inputs to programs using the STDIN textbox under the I/O tab. Following is a sample program which takes name as input and print your name with hello.

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

int main() 
{
    string name;
    cout << "Enter name:";
    getline (cin, name);
    cout << "Hello " << name;
    return 0;
}

About C++

C++ is a widely used middle-level programming language.

  • Supports different platforms like Windows, various Linux flavours, MacOS etc
  • C++ supports OOPS concepts like Inheritance, Polymorphism, Encapsulation and Abstraction.
  • Case-sensitive
  • C++ is a compiler based language
  • C++ supports structured programming language
  • C++ provides alot of inbuilt functions and also supports dynamic memory allocation.
  • Like C, C++ also allows you to play with memory using Pointers.

Syntax help

Loops

1. If-Else:

When ever you want to perform a set of operations based on a condition If-Else is used.

if(conditional-expression) {
   //code
}
else {
   //code
}

You can also use if-else for nested Ifs and If-Else-If ladder when multiple conditions are to be performed on a single variable.

2. Switch:

Switch is an alternative to If-Else-If ladder.

switch(conditional-expression){    
case value1:    
 // code    
 break;  // optional  
case value2:    
 // code    
 break;  // optional  
......    
    
default:     
 code to be executed when all the above cases are not matched;    
}

3. For:

For loop is used to iterate a set of statements based on a condition.

for(Initialization; Condition; Increment/decrement){  
  //code  
}

4. While:

While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.

while (condition) {  
// code 
}

5. Do-While:

Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.

do {  
 // code 
} while (condition);

Functions

Function is a sub-routine which contains set of statements. Usually functions are written when multiple calls are required to same set of statements which increases re-usuability and modularity. Function gets run only when it is called.

How to declare a Function:

return_type function_name(parameters);

How to call a Function:

function_name (parameters)

How to define a Function:

return_type function_name(parameters) {  
 // code
}