Write pseudo-code first if this helps you. Pseudocode is a way of writing down ideas without worrying about syntax of the language that you're trying to utilize.
For instance, the body of your program could be thought of like this:
Display Menu for user
Get user selection
Input data
Process data
Print output
<terminate>
As far as what algorithms to prepare, think of that in this way. Algorithms are implemented inside of functions. Functions can also be thought of as "verbs." In the function implementations, the algorithms you use will utilize data members, which can otherwise be thought of as "nouns."
If verb and noun are alien terms to you, a verb is "an action" and a noun is "a person, place, or thing." Note that every one of the pseudocode statements I wrote has a VERB in the statement. This should hint that those major themes are FUNCTIONS.