Thread: String to Numeric Value

Yes. I would call it <yikes!>, but you're a beginner, and I'm being nice here.

Char's have a value that is "bumped up" by ascii. So a '1' for instance, is not a 1 in ascii. You know all this. C has more than one way to swap char values for int values, and both values for hex values, and octal values, and on and on.

You're HexValue function is re-inventing the wheel. I'm not saying it's not an OK logic/code puzzle to figure out, but it seems like it's such an uninteresting puzzle to spend time on.

When I saw your devotion to the HexValue function, I stopped reading this thread for awhile. I'll go back and re-read the problem, and get you nudged into something more practical -- unless of course, you want to continue working on this HexValue, as a puzzle.

I would suggest changing the entire string to a number via atoi() or strtoi(). Both functions can convert with a change in the last letter of the function name, to long int's, etc. strtoi() also has the extra ability to convert to different number bases, (not just the normal base 10).

Either one should be able to do what you want, in one or two lines of code.

If that is NOT what you want, give me a step by step simple example of exactly what you want: input, and output.

Originally Posted by rwagstaff

I'm just amazed at the relative barbaric nature of C. I've done a little programming in ASP VBScript, Excel/Word Macro languages and this C language is like pulling teeth. Doing simple things are like monumental tasks. I don't doubt the power of C after all the Mars Lander Curiosity is completely programmed using C. Of course, this exercise is for college and I think they like to make you figure out how exactly the language works versus just giving you the tools and letting you program away. Any help is appreciated.

C is much older than all of the languages you listed, and despite C being called a "high-level language", it was designed for relatively low-level tasks like systems programming. This exercise does sound pointless on its own (because C has functions like strtol that do what you want already), but apparently your college class wants you to figure out how to do this particular task without using any built-in function. You shouldn't blame C for that. Blame your instructor. :P

Edit: Adak: strtoi is a non-standard function (it doesn't exist in the standard library). strtol can be used instead, and its return value can be cast to int if needed.

You'd be better off using the other technique mentioned above using the values from the ASCII chart and doing a simple math equation. You'd save yourself about 65 line and get rid of the switch. Posts #2-6.

Originally Posted by WaltP

And when you get to the next language that doesn't have an strtol-like function, you are a cripple.

You missed my point: since the function exists in the standard library, you should use it unless you have a special reason to do otherwise (learning how to implement it being one of the legitimate special reasons).

Originally Posted by WaltP

I've never had a function like that in any other language I've used, and I have never used that function in over 25 years of professional C work.

I have seen functions like that in other languages that I have used, and some of them are even part of the core language, but so what? Yes, a programmer should learn how to implement something as basic as this, but if there is the need to convert a string to long (or int), the standard library function should be preferred, so grumpy mentioning strtol an option for (future) use makes sense. Unless you're telling me that you only use your own personal library that duplicates the functionality in the standard library?

Originally Posted by rwagstaff

Please review the function below

You do not need all the break statements because you are already returning a value before each of them. You can also make use of follow through, e.g.,

Code:

case 'A':
case 'a':
    return 10;

Originally Posted by rwagstaff

What's a good web site that has a C function reference?

Are you using an introductory book? It may have such a reference for you. That said...

Originally Posted by rwagstaff

Of course, this exercise is for college and I think they like to make you figure out how exactly the language works versus just giving you the tools and letting you program away.

... you should learn both how to use the tools and how the tools work. The "how the tools work" part is the crux of WaltP's objection in post #12. Based on your assignment requirements ("using 2's complement"), it does sound like the point here is to learn how the tools work, rather than this being just incidental to completing your assignment.

After you remove those breaks, your HexValue function would be acceptable, but you really don't gain much from using that switch instead of WaltP's suggestion. As iMalc stated, the digits are guaranteed to be in sequence from '0' to '9'. It isn't actually guaranteed that 'A' to 'F' will be in sequence, but ASCII or an ASCII based character set is very likely to be what you'll ever use, so that isn't a realistic problem.

Originally Posted by rwagstaff

What's a good web site that has a C function reference?? Basic definitions, use, examples and the like.

I use the The GNU C Library Reference Manual. It has some Posix(Unix) extensions which I find quite useful. Functions that are non-ansi(or require the gcc compiler) will be clearly marked as so. Download the PDF and check it out. It's great.

The GNU C Library - GNU Project - Free Software Foundation (FSF)

Originally Posted by rwagstaff

I'm just amazed at the relative barbaric nature of C.

Hahaha. I'll give you a like just for this sentence.

Originally Posted by rwagstaff

I'm just amazed at the relative barbaric nature of C.

Nah, barbaric would be manually pushing electrons around.
C is at least a couple of levels of abstraction above that!

Originally Posted by WaltP

And when you get to the next language that doesn't have an strtol-like function, you are a cripple. C is not the only language out there. and presumably is not the last one to be learned.

I've never had a function like that in any other language I've used, and I have never used that function in over 25 years of professional C work. Knowing how to do something has helped me greatly.

It clearly hasn't helped you develop either manners or common sense though.

I simply named a function in the C standard library that was directly relevant to the original problem, and did not insult anyone who offered an alternative technique.

Yes, there is value in knowing how to do things. There is also value in knowing how to reuse existing facilities. I would suggest that someone who does not understand reuse is exaggerating in describing himself or herself as a professional.