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

19 Apr, 2018
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().
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