I need a little help with solving this practice problem

Using C/C++, write a recursive functionand a function of iteration respectively.Both function calculate and return the following sequence. The sequence S satisfies the following recurrence relation: the first three number of the sequence is 0, 1, 2, from the 4th one, each number is equal to the sum of its preceding three numbers; i.e., given position n4, the nth S sequence number is:

S(n) = S(n-1) + S(n-2) + S(n-3) Note: in main(), you need to call the functions by passing only the position number n.