Lamda_Expression_4.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;

// Function to print vector
void printVector(vector<int> v)
{
	// lambda expression to print vector
	for_each(v.begin(), v.end(), [](int i) {cout << i << " ";} );
	cout << endl;
}

int main()
{
	vector<int> v {4, 1, 3, 5, 2, 3, 1, 7};
	printVector(v);

	// below snippet find first number greater than 4 find_if searches for an element for which function(third argument) returns true
	vector<int>:: iterator p = find_if(v.begin(), v.end(), [](int i){return i > 4;} );
	cout << "First number greater than 4 is : " << *p << endl;

	// function to sort vector, lambda expression is for sorting in non-increasing order Compiler can make out return type as bool, but shown here just for explanation
	sort(v.begin(), v.end(), [](const int& a, const int& b) -> bool {return a > b;} );
	printVector(v);

	// function to count numbers greater than or equal to 5
	int count_5 = count_if(v.begin(), v.end(), [](int a) {return (a >= 5);} );
	cout << "The number of elements greater than or equal to 5 is : "<< count_5 << endl;

	// function for removing duplicate element (after sorting all duplicate comes together)
	p = unique(v.begin(), v.end(), [](int a, int b) {return a == b;} );
	// resizing vector to make size equal to total different number
	v.resize(distance(v.begin(), p));
	printVector(v);

	// accumulate function accumulate the container on the basis of function provided as third argument
	int arr[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
	int f = accumulate(arr, arr + 10, 1, [](int i, int j) {return i * j;} );
	cout << "Factorial of 10 is : " << f << endl;

	//	 We can also access function by storing this into variable
	auto square = [](int i) {return i * i;};
	cout << "Square of 5 is : " << square(5) << endl;
}