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From: Ar Rakin <rakinar2@onesoftnet.eu.org>
Newsgroups: comp.lang.c
Subject: Re: Oh d-ai-ry d-ai-ry me
Date: Tue, 3 Jun 2025 22:06:50 +0600
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On 5/31/25 2:01 AM, Richard Heathfield wrote:
> This evening I accidentally bumped into a chatbot, and I wondered 
> whether it was any good at C programming.
> 
> I was impressed when it solved Goldbach's Conjecture (admittedly for 
> small n) and 5-disc Hanoi, but then I thought back to a recent thread 
> here (which I have no intent of resurrecting), so I asked it if it could 
> have saved me a job if I'd only asked it a few hours ago.
> 
> Judge for yourselves!
> 
> I asked: "Write a program that is valid C90 but invalid C99."
> 
> ChatGPT said:
> 
> Certainly! To illustrate this, I'll write a C program that is valid in 
> C90 but invalid in C99. The key difference between C90 and C99 revolves 
> around variable declaration and initialization.
> Key Issue:
> 
>      In C90, variables can only be declared at the beginning of a block 
> (before any executable code).
> 
>      In C99, variables can be declared anywhere within a block, even 
> between statements.
> 
> C Program Example:
> 
> This program is valid in C90 but invalid in C99 because the variable x 
> is declared after executable code.
> 
> #include <stdio.h>
> 
> int main() {
>      printf("Hello, world!\n");
> 
>      int x = 5;  // Declaration after executable code (invalid in C99)
> 
>      printf("x = %d\n", x);
>      return 0;
> }
> 
> Why it’s Valid in C90:
> 
>      In C90, all variable declarations must appear at the beginning of a 
> block (before any code). This program would be valid in C90 because x is 
> declared after the printf statement, but only the declaration of x 
> itself breaks the rule in C99.
> 
> Why it’s Invalid in C99:
> 
>      In C99, variables can be declared anywhere within a block, even 
> after executable statements (not just at the beginning of a block). This 
> is why the above code would cause an error in C99, as the variable x is 
> declared after a statement (printf).
> 
> Compilation Example:
> 
> If you compile this program with a C99 compiler (e.g., GCC), you'll get 
> an error similar to this:
> 
> error: variable 'x' declared after statement
> 
> To summarize:
> 
>      C90 allows this style (declaration after code).
> 
>      C99 does not allow it, so the program becomes invalid.
> 

This is the reason why I tell people who write code that AI/LLMs can't 
ever replace them like this.  AI tools can only be a tool that you use. 
To write code, you'd still need to know something by yourself at the end 
of the day.

-- 
Rakin