Thread: Menu type system flow-control

The best way to do this is to use a loop of some sort. For example:

Code:

int main() {
    int n;

    do {
        printf("Type 1 for this, 2 for that, -1 to quit: ");
        scanf("%d", &n);
        switch(n) {
            /* ... */
        }
    } while(n != -1);

    return 0;
}

Originally Posted by drag0n69

I see. So I assume the return 0; means it will start the loop all over again?

Not exactly. The return 0 exits from main() and ends the program. The loop goes from "do" to "while". Perhaps you should read this tutorial. http://www.cprogramming.com/tutorial/c/lesson3.html

A do-while or while loop, in essence, continues executing its contents over and over again while some condition is true. For example:

Code:

int x;
printf("Enter a number, but please, not zero: ");
scanf("%d", &x);
while(x == 0) {
    printf("I said, \"not zero\"! Try again: ");
    scanf("%d", &x);
}

I also have another question related to this program...
This is an assignment for a course I am taking and the restrictions are that I have to make each task in the menu a function of its own. There are tasks such as "print all multiples of a number" or "change the value of a variable". However; I am not supposed to use any global variables. Does this mean I have to use pointers?

No; not necessarily. Have you learned about functions? They have a way to pass information in, via parameters, and a way to pass information out, via return values. The only trouble is, you can only pass out one return value. So if you need to return more than one variable, you probably need to use pointers. (You can use other hacks, like returning a structure, but never mind that.) Another reason to use pointers is that passing information in and out means making possibly unnecessary copies of that information. If the variables and types involved are quite large, it can be more efficient to pass pointers.

(Remember the "return 0" in main? That was main passing information to whatever executed your program -- probably Windows -- telling it that your program executed successfully. Returning 1 usually indicates that your program encountered an error.)

But until you get to structures -- there's no need to use pointers. Passing simple variables "by value" in and returning them back again is quite efficient.

So -- you need to read up on parameters, return values, and functions in general. Your textbook undoubtably has some information on this topic, and there are many tutorials of this sort on the web. Here's one of them. http://www.cprogramming.com/tutorial/c/lesson4.html

And for example; if there was a function to print the first 10 multiples of an integer; should I make the function calculate all the multiples at once and store them in an array? Or should I make the function to simply give the next multiple? Which way would be more efficient?

Thanks!

There's no need to use an array if you can just print the information after you've discovered it. It's easier that way.

Sure, something like that would work. e.g.

Code:

int timesthree(int x) {
    return x * 3;
}

x = 3;
while(x <= 12) {
    printf("&#37;i\n", x);
    x = timesthree(x);
}

However, I think you are perhaps over-complicating things. I quote:

There are tasks such as "print all multiples of a number" or "change the value of a variable".

If all you want to do is print all multiples of a number, you could use a function like

Code:

void print_multiples(int number, int min, int max);

and do everything in there. (Set x to min, increment by number until x is max, print the number each time.) Changing the value of a variable between different functions isn't necessary in this case. (Passing variables is -- unless you want the function to always print multiples of 3 between 3 and 12 -- but return values isn't really.)

But of course, when you get around to implementing the "change the value of a variable", you probably will be using return values and stuff.