Simple doubt in C | Together C & C++ | Page 1

scenic thunder Oct 30, 2024, 3:54 PM

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Is *p=&a an invalid statement in c??

storm parrotBOT Oct 30, 2024, 3:54 PM

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serene hatch Oct 30, 2024, 3:59 PM

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the syntax is correct, the question would be about p and a types

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as p would have to be a pointer to a pointer to a type of a

cyan cove Oct 30, 2024, 4:18 PM

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Obligatory nitpick that *p=&a isn't a statement in the first place, it's an expression. *p=&a; would be a statement ackchyually

simple thorn Oct 30, 2024, 4:27 PM

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cyan cove Obligatory nitpick that `*p=&a` isn't a statement in the first place, it's an ex...

BOOOOOOOOM!!!!

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so, then that just means the answer to his question is yes

simple thorn Oct 30, 2024, 4:29 PM

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scenic thunder Is *p=&a an invalid statement in c??

.... im assuming your reason for asking this question is that you have a program that uses it and the program doesnt compile or doesnt work.

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........ can we see the program

languid hawk Oct 30, 2024, 4:58 PM

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.. or a test question on an exam

simple thorn Oct 30, 2024, 5:24 PM

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💀

scenic thunder Oct 31, 2024, 2:42 AM

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simple thorn .... im assuming your reason for asking this question is that you have a program...

Well, I didn't write any program, it's just a doubt rised in my mind while studying. Also when I asked chatgpt about this , it said it is invalid..... .....

simple thorn Oct 31, 2024, 2:44 AM

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Oh

scenic thunder Oct 31, 2024, 2:44 AM

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Another doubt is that, *p points to the value at the address it holding. So does that mean *p=&a; the variable 'a' store the address of itself?????

simple thorn Oct 31, 2024, 2:44 AM

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So either chatgpt is very imperceptive

simple thorn Oct 31, 2024, 2:44 AM

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cyan cove Obligatory nitpick that `*p=&a` isn't a statement in the first place, it's an ex...

Or it's very perceptive

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And you have experienced the AI equivalent of HolyBlackCat explaining to you that it isn't a statement because there's no semicolon and a statement is <expression>;

scenic thunder Oct 31, 2024, 2:47 AM

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Hey @simple thorn can u explain my second doubt if u don't mind.......

simple thorn Oct 31, 2024, 2:48 AM

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scenic thunder Another doubt is that, *p points to the value at the address it holding. So does...

So basically, *p has to be a pointer to whatever type a is since we're assigning to it &a

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.... that means p is a pointer to pointer to whatever type a is

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so,

scenic thunder Oct 31, 2024, 2:48 AM

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Ysss

simple thorn Oct 31, 2024, 2:49 AM

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;compile ```c
int a;
int *q;
int **p;

p = &q;
*p = &a;

slow meteorBOT Oct 31, 2024, 2:49 AM

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Compilation successful

No output.

simple thorn Oct 31, 2024, 2:49 AM

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.... q is now pointing to a

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We caused it to point to a indirectly via p

scenic thunder Oct 31, 2024, 2:50 AM

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So here in this codee........

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P holds the address of q. So the last statement means q stores the address of the variable 'a'

simple thorn Oct 31, 2024, 2:51 AM

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Yup

scenic thunder Oct 31, 2024, 2:52 AM

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But chatgpt said something else let me read it wait a sec

simple thorn Oct 31, 2024, 2:52 AM

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Well ChatGPT can go die in a ditch I guess

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It points to a

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No doubt about it

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;compile ```c
int a;
int *q;
int **p;

p = &q;
*p = &a;

//Does q point to a? Let's find out!
*q = 69;
printf("%d\n", a);

slow meteorBOT Oct 31, 2024, 2:53 AM

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Program Output

scenic thunder Oct 31, 2024, 2:53 AM

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I will just screenshot it.....wait

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Waittt

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No, *p = &a does not mean that 'a' will store its own address. In fact, this expression is incorrect in C and will either cause a compiler error or undefined behavior. Let me explain why.

Key Concepts to Understand

p is a pointer variable that stores the address of another variable.
*p is used to dereference the pointer, meaning it gives you access to the value stored at the memory address that p points to.
&a is the address of the variable a.

Why *p = &a is Wrong

*p expects a value of type int (because p is a pointer to an int).

But &a is an address (type int *), not an int value.

So, assigning &a to *p is type-incompatible.

simple thorn Oct 31, 2024, 2:56 AM

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So, *p = &a is basically saying "Make the pointer pointed to by p point to a.

simple thorn Oct 31, 2024, 2:58 AM

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scenic thunder No, *p = &a does not mean that 'a' will store its own address. In fact, this exp...

So, this means that either you told chatgpt that p is a pointer to int, or chatgpt pulled that assumption out of nowhere and is wrong.

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Could be either

scenic thunder Oct 31, 2024, 2:59 AM

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simple thorn So, this means that either you told chatgpt that `p` is a pointer to int, or cha...

Yss I told p is pointer int type...

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Now I c.......

simple thorn Oct 31, 2024, 2:59 AM

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Oh

scenic thunder Oct 31, 2024, 2:59 AM

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So basically answer to my question is it's a legal statement....

simple thorn Oct 31, 2024, 2:59 AM

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Expression*

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But yes

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There's no way p is a pointer to int though.

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It could be a pointer to pointer to int.

scenic thunder Oct 31, 2024, 3:00 AM

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Wait I didn't understand.....

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Ok ok now I understand....

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Thankuuuu

slow meteorBOT Oct 31, 2024, 3:08 AM

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Hello! I can compile code for you. To compile code, use the ;compile command. type ;help compile for more information.

If you are unfamiliar with Markdown, codeblocks can be created by formatting your message as the following.
```
<code>
```

scenic thunder Oct 31, 2024, 3:09 AM

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!solved

storm parrotBOT Oct 31, 2024, 3:09 AM

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Thank you and let us know if you have any more questions!

This thread is now set to auto-hide after an hour of inactivity

scenic thunder Oct 31, 2024, 3:10 AM

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;compile
```
int *p,a=10;
*p=&a;
```

slow meteorBOT Oct 31, 2024, 3:10 AM

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Critical error:

You must attach a code-block containing code to your message or quote a message that has one.

serene hatch Oct 31, 2024, 11:26 AM

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@scenic thunder, if you want to learn something, you start by banning yourself from chatgpt and other kind of language models, also using chatgpt as argument "it told me something else" is irrelevant in any technical discussion with actual at least semi-intelligent beings :P

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nogpt

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buy a book™

serene hatch Oct 31, 2024, 11:29 AM

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scenic thunder ;compile \`\`\` int *p,a=10; *p=&a; \`\`\`

PS that block contains backticks ` preceeded by backslashes, that won't work, as backslash is to make them visible instead of using their assigned meaning, so for code block those just have to be three backticks

scenic thunder Oct 31, 2024, 3:40 PM

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serene hatch PS that block contains backticks \` preceeded by backslashes, that won't work, a...

Yeahhh I was tryna using the bot😅 failed....

#Simple doubt in C