How can I avoid using goto for a series of prompts?

Question

I'm writing a console based application that prompts a user for a series of questions. E.g:

"Enter a record to open:"

"Do you want to do X?"

"Do you want to do Y?"

"Are you sure you want to continue?"

If the user enters nothing at any prompt I want to go up one level. This is easy using goto. The only other way I can think of to do it is nested for loops which looks far uglier and gets pretty unwieldy for more than a couple of prompts. There must be an easy way to do this though, I just can't think of it.

Answer 1

Can you use a switch() statement to handle your cases with the default being going up the one level?

Answer 2

Write it recursively instead of iteratively.

Answer 3

You're basically writing a very simple state machine - use functions to represent every state: (I'll use random pseudocode, since you didn't specify a language)

get_information():
    return get_record()

ask_record():
    record = read_line()
    return () if !record
    return ask_y(record)

ask_x(record):
    x = read_line()
    return ask_record() if !x
    return ask_y(record, x)

ask_y(record, x):
    y = read_line()
    return ask_x(record) if !y
    return ask_continue(record, x, y)

ask_continue(record, x, y)
    continue = read_line()
    return ask_y(record, x) if !continue
    return (record, x, y)

this is a trivial approach. In some languages the call stack will grow, in others it won't. If you have a language which causes the stack to grow, you can use trampolines to prevent it, by rewriting get_information to do:

x = get_information
while x is function:
    x=x()
return x

ask_x(record):
    x = read_line()
    return (lambda: ask_record()) if !x
    return (lambda: ask_y(record, x))

Or even abstracting the question and memory address of result in some question structure:

struct question {
    question *next, *prev;
    char prompt[];
    char **result;
}

and then running in a loop, calling question* run_question(question*), going to ->next, or ->prev depending on the answer, until the result is NULL (as a stop condition, when results are filled in and no questions are left).

The last solution is probably the most "normal one" if you use an imperative language with direct pointer access.

Answer 4

write it as a simple state machine.

while(running)
{
    if (state == INIT)
    {
        out("enter record");
        state = DO_X;
    }
    else if (state == DO_X)
    {
        do whatever for x.
        state = WHATEVER_NEXT_STATE_IS;
    }
}