STL-05 Array algorithms in C++ STL

Array algorithms in C++ STL (all_of, any_of, none_of, copy_n and iota)

From C++11 onwards, some new and interesting algorithms are added in STL of C++. These algorithms operate on an array and are useful in saving time during coding and hence useful in competitive programming as well.

all_of()

This function operates on whole range of array elements and can save time to run a loop to check each elements one by one. It checks for a given property on every element and returns true when each element in range satisfies specified property, else returns false.

// C++ code to demonstrate working of all_of()
#include<iostream>
#include<algorithm> // for all_of()
using namespace std;
int main() {
	// Initializing array
	int ar[6] = {1, 2, 3, 4, 5, -6};

	// Checking if all elements are positive
	all_of(ar, ar+6, [](int x) { return x>0; })?
		cout << "All are positive elements" :
		cout << "All are not positive elements";

	return 0;

}

Output:

All are not positive elements

In the above code, -6 being a negative element negates the condition and returns false.

any_of()

This function checks for a given range if there’s even one element satisfying a given property mentioned in function. Returns true if at least one element satisfies the property else returns false.

// C++ code to demonstrate working of any_of()
#include<iostream>
#include<algorithm> // for any_of()
using namespace std;
int main() {
	// Initializing array
	int ar[6] = {1, 2, 3, 4, 5, -6};

	// Checking if any element is negative
	any_of(ar, ar+6, [](int x){ return x<0; })?
		cout << "There exists a negative element" :
		cout << "All are positive elements";

	return 0;

}

Output:

There exists a negative element

In above code, -6 makes the condition positive.

none_of()

This function returns true if none of elements satisfies the given condition else returns false.

// C++ code to demonstrate working of none_of()
#include<iostream>
#include<algorithm> // for none_of()
using namespace std;
int main() {
	// Initializing array
	int ar[6] = {1, 2, 3, 4, 5, 6};

	// Checking if no element is negative
	none_of(ar, ar+6, [](int x){ return x<0; })?
		cout << "No negative elements" :
		cout << "There are negative elements";

	return 0;
}

Output:

No negative elements

Since all elements are positive, the function returns true.

copy_n()

copy_n() copies one array elements to new array. This type of copy creates a deep copy of array. This function takes 3 arguments, source array name, size of array and the target array name.

// C++ code to demonstrate working of copy_n()
#include<iostream>
#include<algorithm> // for copy_n()
using namespace std;
int main() {
	// Initializing array
	int ar[6] = {1, 2, 3, 4, 5, 6};

	// Declaring second array
	int ar1[6];

	// Using copy_n() to copy contents
	copy_n(ar, 6, ar1);

	// Displaying the copied array
	cout << "The new array after copying is : ";
	for (int i=0; i<6 ; i++)
	cout << ar1[i] << " ";

	return 0;

}

Output:

The new array after copying is : 1 2 3 4 5 6

In the above code, the elements of ar are copied in ar1 using copy_n().

iota()

This function is used to assign continuous values to array. This function accepts 3 arguments, the array name, size, and the starting number.

// C++ code to demonstrate working of iota()
#include<iostream>
#include<numeric> // for iota()
using namespace std;
int main() {
	// Initializing array with 0 values
	int ar[6] = {0};

	// Using iota() to assign values
	iota(ar, ar+6, 20);

	// Displaying the new array
	cout << "The new array after assigning values is : ";
	for (int i=0; i<6 ; i++)
	cout << ar[i] << " ";

	return 0;

}

Output:

The new array after assigning values is : 20 21 22 23 24 25

In the above code, continuous values are assigned to array using iota().