C++, please use provided function prototype

A. Factorial Calculation Use filename: factorial.cpp Write a function that computes the factorial for given integer value by loop iteration. Note - for a given number n, its factorial value is given by n! = 1*2*3*...*(n-1)*n By definition, e! = 1! = 1 The function prototype is given by int factorial (const int &); Function should do following tests on argument value: If argument 1, compute its factorial by iteration and return factorial value