C++ please

A permutation is an arrangement of elements taken from a finite set. The permutation function P(nk) gives the number of different permutations of any k terms taken from set of n terms. The formula for computing the number of permutations is 5. n! P(n,k)=(n-k)! Develop two functions: ntfactorial(int n), that calculates and return factorial of n. double permutation(int n, int k), that calculates and returns permutations. . . Note: Permutations function calls factorial function