Assignment #0 Frequently Asked Questions

Do we need to include a main() function in our files?

For each of the first three problems, you will probably want to write a short main() function to test your function. However, you don't need to submit your main(); all we're concerned about is the one function we asked for. In fact, it would be easier on the marker if you did not include a main() with your electronic submission.

In one of the problems I want to use a char variable as an array subscript, but I get a compiler warning.

Are you sure what you're doing is meaningful? If so, then your compiler is just being over-protective in this case. You can ignore this warning, and the marker will too. If you want the warning message to go away, prefix the variable with an (int) typecast. (Typecasting will be covered on 29 May.)

How do we do I/O for the first three problems?

You don't. The functions do their "input" and "output" through parameter passing and return values.

How do I gracefully handle fatal (i.e., non-recoverable) errors?

Read up on the standard library's exit() function.

Why doesn't the following code work?
double *p;
scanf("%lf", p);

You are using an uninitialized pointer in your call to scanf(). You need a double variable in which to store the value returned by scanf(), and p is not a double; it's a pointer to a double. The above code would work if p were actually pointing to a double variable, but it's not.

When I read numbers from the keyboard with scanf("%d ",...) it seems to hang.

The whitespace in the format string tells scanf() to continue reading characters until it reaches a non-whitespace character. Thus with the above format string, scanf() will not return until you've actually entered two pieces of data (an int plus possibly some whitespace plus something else). This is probably not what you want. Try scanf("%d",...) instead.

I'm trying to use malloc() to dynamically allocate space for an array and am having problems with...

You don't need to use malloc() for this assignment as we haven't yet covered dynamic memory management. Please just use regular (static) arrays. You won't get any bonus marks for using dynamic allocation; in fact, you'll probably lose marks if you don't use malloc() correctly (which seems to be the case quite often, judging from the code people have sent me).

I'm having trouble reading an EOF with scanf().

Are you sure you're checking the return value of scanf()? Remember that it's a function returning int. Read the man page for scanf() to see what the return values signify.

OK, I'm checking the return value of scanf(), but sometimes my program seems to be ignoring a CTRL-D unless I press it a couple of times.

It is a quirk of some systems (due to input buffering) that EOF is not recognized as such unless it is the first character of a new line, or is pressed twice in a row. Don't worry about this quirk; just make sure that your program properly handles an EOF when it's able to see one (i.e., when it is returned by scanf()).