Lamda_Expression_5.cpp

// C++ program to demonstrate lambda expression in C++
/*
A lambda expression can have more power than an ordinary function by having access to variables from the enclosing scope. We can capture external variables from the enclosing scope in three ways : 
      Capture by reference 
      Capture by value 
      Capture by both (mixed capture)
Syntax used for capturing variables : 
      [&] : capture all external variables by reference 
      [=] : capture all external variables by value 
      [a, &b] : capture a by value and b by reference
A lambda with an empty capture clause [ ] can only access variables which are local to it. 
*/


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

int main()
{
	vector<int> v1 = {3, 1, 7, 9};
	vector<int> v2 = {10, 2, 7, 16, 9};

	// access v1 and v2 by reference
	auto pushinto = [&] (int m)
	{
		v1.push_back(m);
		v2.push_back(m);
	};

	// it pushes 20 in both v1 and v2
	pushinto(20);

	// access v1 by copy
	[v1]()
	{
		for (auto p = v1.begin(); p != v1.end(); p++)
		{
			cout << *p << " ";
		}
	};

	int N = 5;

	// below snippet find first number greater than N [N] denotes, can access only N by value
	vector<int>:: iterator p = find_if(v1.begin(), v1.end(), [N](int i)
	{
		return i > N;
	});

	cout << "First number greater than 5 is : " << *p << endl;

	// function to count numbers greater than or equal to N [=] denotes, can access all variable
	int count_N = count_if(v1.begin(), v1.end(), [=](int a)
	{
		return (a >= N);
	});

	cout << "The number of elements greater than or equal to 5 is : "
		<< count_N << endl;
}