(using c programing recursion)

Multiplication with only addition and subtraction.

Write a function for mutliply(a, b), where a and b are both positive integers, but you can only use the + or operators.

Reverse string

Write a recursive function to reverse a string.

Permutations

Write a function that take an integer parameter n and prints all n! permutations of the n letters starting at a (assume that n is no greater than 26). A permutation of n elements is one of the n! possible orderings of the elements. As an example, when n = 3 you should get the following output (but do not worry about the order in which you enumerate them):

bca cba cab acb bac abc

What to turn in

Source code that contains the functions, along with some test code in main function for each function.