My instructor wishes for me to construct prototypes for a small program but I'm having a time figuring this out. help please.

// interest.cpp

// Date: Feb 25, 2008

// Calculate the simple interest on a loan for 1 year given the amount and rate

#include<iostream>

#include<iomanip>

using namespace std;

Code://Prototypes hereint main() { // declare variables // get user input // call function for calculation // display results return 0; } double calcint(double amount, double rate) { return amount * rate * 1; }