what is throw in c 2b 2b

1#include <stdexcept>
2
3int compare( int a, int b ) {
4    if ( a < 0 || b < 0 ) {
5        throw std::invalid_argument( "received negative value" );
6    }
7}

1//throw "throws" an exception.
2  
3It is usually used like:
4
5if(something isnt right){
6  throw somethingee;
7}
8
9/*(std::)*/cout << somethingee;

1// using standard exceptions
2#include <iostream>
3#include <exception>
4using namespace std;
5
6class myexception: public exception
7{
8  virtual const char* what() const throw()
9  {
10    return "My exception happened";
11  }
12} myex;
13
14int main () {
15  try
16  {
17    throw myex;
18  }
19  catch (exception& e)
20  {
21    cout << e.what() << '\n';
22  }
23  return 0;
24}