Re: [PIC] Learning C

Hi Colin,

You might be intested to know that to check for floating point errors / 
exceptions in C you would use:

if (x == x)...
or
if (x != x)...

where x is a float

e.g.
 	float	x

 	x = 1.0 / 0.0;

 	if (x != x)
 	{	// x is a NaN which is an error
 	}

Here clearly "x 'is the same as' x" but the test is "x 'is a NaN'".

Friendly Regards
Sergio

On Sun, 10 Nov 2024, CDB wrote:

> I have always separated the difference of =  and == in C by referring to the 
> latter as 'is the same as'
>
> if (X is the same as Y) then ......  if (X == Y) then
> x = y       x now contains the value of Y.
>
> Colin
>
>
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> On 11/11/2024 08:24:15, "smplx" <[email protected]> wrote:
>
>> 
>> 
>> On Sun, 10 Nov 2024, Neil wrote:
>> 
>>> Agree with a couple things from other comments such as C being high-level 
>>> assembler and using a PC at first (you can just use gcc already on Linux).
>>> 
>>> Already knowing a structured language is very helpful.
>>> But IMO you'll have to wrap your head around pointers, which can get 
>>> confusing. I find this C visualizer very helpful for figuring out some 
>>> algorithm... https://pythontutor.com/c.html
>>> 
>>> One more note: = != ==
>>> Or in other words, the equal sign ( = ) and the double equal size ( == ) 
>>> are very different things in C. The first assigns a value and the other 
>>> compares values. But people new to C will invariably use a single equal 
>>> for a comparison and the code is true every time, as C will compile it as 
>>> valid code, do the assignment, then the comparison. You have been warned 
>>> ;P
>> 
>> Sorry to wade in here but:
>> 
>> if (y = x)...
>> 
>> assigns x to y then compares the result to 0. 0 is nomally taken to
>> mean false and "not 0" as true. So it is almost alway true except in the 
>> case where x is 0.
>> 
>> I'm not sure what happens if x and y are floats and x is a NaN or if x and 
>> y are structures.
>> 
>> if you're looking for a real headache try debugging a program that 
>> contains:
>> 
>> if (! x == y)...
>> 
>> Trying to learn C on bare metal is like trying to learn to fly by crashing 
>> a lot. It's a lot quicker and easier if you learn on a simulator.
>> 
>> Friendly Regards
>> Sergio Masci
>> 
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