[nfbcs] Can someone please help me understand what I'm doing wrong?

[Mike Gorse]

Hi Lanie,

You have
float *pAccount;
which defines a pointer to a float. Then
compareBalances(account1, account2, **pAccount);

The **pAccount is causing an error since pAccount is defined as a float *. 
You're trying to dereference pAccount (which isn't what you want to do 
here in the first place--pAccount hasn't been initialized, so reading from 
the address pointed to by it would segfault), but, regardless, 
dereferencing it would give a float, and the second * indicates that you 
want to dereference the float, which you can't do, since a float is not a 
pointer.

Also, I don't think that compareBalances really does what you want it to 
do. It accepts account1 and account2 *by value*, so, if you call it, then 
the following would happen, more or less:
- the value of account1 would be pushed to the stack
- the value of account2 would be pushed to the stack
- The function would return the address on the stack at which account1 or 
account2 are stored
- Now that the function has returned, anything pointing to its stack can 
no longer be considered valid. It points to memory that will be written 
over the next time you call a function.

Maybe you wanted compareBalances to take pointers as its parameters?

I hope that I have explained all of this clearly; if you're learning about 
pointers, then you need to have the foundation in terms of understanding 
how they work and what happens underneath when a function is called.

On Thu, 9 Nov 2017, Lanie Molinar via nfbcs wrote:

> Hi. Sorry about that. I wish there was a simpler way to do this than 
> writing two completely different emails. I did what you suggested, but 
> I'm still getting an error that I don't understand. You should be able 
> to see my updated code with the link I sent earlier, but I'll add it 
> just in case. I'll also share a link to my PuTTY log. Thanks.
>
> Code: https://1drv.ms/u/s!AjYDVzgAcL7ohaIYqSQEmqyOEZprZQ
>
> Log: https://1drv.ms/u/s!AjYDVzgAcL7ohY4Gkm1OCnzSLxHYUg
>
>
> On 11/9/2017 5:04 PM, Jim Barbour via nfbcs wrote:
>> Howdy,
>>
>> I'd appreciate it if you didn't cross post like this.  It makes it harder 
> to reply if you're not on both lists.
>>
>> In the compareBalances function, pAccount needs to be a float **,
>> because you're going to assign a value to a pointer and have it seen
>> outside the function.  So, change float * pAccount to float ** pAccount
>> and change the pAccount = ... statements to be *pAccount = ...
>>
>> Hope this helps,
>>
>> Jim
>>
>> On Thu, Nov 09, 2017 at 10:38:05PM +0000, Lanie Molinar via nfbcs wrote:
>>> Hi, everyone. I’m working on an assignment where I’m learning how to use 
> pointers. I think I almost have it but Sam’s and Sue’s balances keep showing 
> up as 0.00 at the end. Can you please help? I’ll keep working on it, too. 
> Thanks.
>>>
>>>
>>> Sent from Mail<https://go.microsoft.com/fwlink/?LinkId=550986> for Windows 
> 10
>>>
>>
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