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[Closed] Beginner's C++ help - function order

PJay · 2010-01-27T17:35:40Z

Many years ago I used to rather enjoy tinkering with computer programming (I was never any good but that wasn't really the point). I learnt using Basic, had some Cobol training, tinkered with some assembly language (badly) and (fortunately) played around with a language called [b]E[/b] on the Commodore Amiga (which I think was based on C and was an object orientated, function based, compiled language on a GIMP multitasking system, so I'm not as completely in the dark as I would be coming to C++ from, say, Sinclair Basic). That was all a long time ago (it's probably about 15 years since I played around with the E language) but I've decided to see if I can re-ingnite that interest by playing around with C++ (with no other purpose that to have some fun and perhaps learn a useful, if limited, skill). So, I'm equipped with Microsoft Visual C++ Express and a copy of Teach Yourself C++ in 24hrs by Sams. True to form I started with the "Hello World" program running as a console application - and it worked. The next step was an introduction to functions (as I used to use in E) which is where I ran into my first issue. The demo function program simply printed "Hello World" to the console from the [b]Main()[/b] function, called a second function which printed out a second message to the console, returned and exited; simple stuff. Rather than type it verbatim from the book I set it up myself and it went a bit wrong. In the book example the called function came first in the source code, followed by [b]main()[/b] (although I don't remember any reason being given to explain this). There were 2 errors, the first was obvious, despite definining the called function as [b]void[/b] I tried to return 0 (I don't think that E required parameters to be defined) and was easily sorted. The second had me a bit flumoxed and said that the function identifier wasn't defined (for the called function) on the line where it was called. After much checking that I'd got the function name in the call line identical to the function name in the signature I was getting a bit flustered but decided to mirror the book example and put the called function first in the source code - lo and behold, it worked. So the compiler choked trying to call a function that wasn't defined at the point of being called and raised an error but, interestingly, then continued with the compile and then complained (initially) that the called function was a void function returning a value, so it clearly realised that the called function was there and was a function, and so should have had all the information necessary to successfully compile the program, but didn't. Now E (and the assemblers I've played with) was, if I remember rightly, described as two pass, in that the compiler parsed the source code in two distinct phases; part of the function of the first pass was to identify function names (or in the case of assemblers, lables) for the second pass in which the actual compiling occured. Microsoft Visual C++ appears to compile in one pass. I'm going on a bit but essentially I wanted to know whether I have to arrange all my functions in a C++ program's source code so that they are arranged in an order where they're defined prior to the first instance of them being called - essentially putting main() at the end of the program in order for the compile to complete. In E I always put the main() function first and called functions below this (possibly a hangover from interpreted Basic which program execution always began from the first line of source code). Perhaps it's considered bad practice to define functions after the first instance of they're being called and C++ forces this order to encourage a certain thought process to occur before coding, but the blurb in the introduction to the C++ book suggested that C++ was meant to be flexible to allow programs to program in the style they wished. Perhaps it's a foible of Microsoft C++ (the book works with a Borland compiler) and there's a way to set it up as a two pass compiler. Anyway, do I need to stick to this way of ordering source code or should I be able to start my source code with main() and stick my function definitions where I like (in E I'm pretty sure that the idea of functions as self contained elements meant that they could go in in any order you liked)? I was always a pretty poor hobbyist programer and I'll probably never write anything useful (and there's certainly a long way to go and a lot to learn from "Hello Word!" in a console window to a windowed Windows application using the .net framework - and I've now idea about this) but I didn't expect to get quite so muddle at the "Hello World" stage.

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GrahamS

Posts: 31206

Full Member

Yeah the syntax and general style makes it easy enough to jump between them if you're a decent programmer (which you obviously are) but there still some fairly fundamental differences - more than say C to C++ I'd say.

Posted : 28/01/2010 6:15 pm

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