I am getting an error telling me I should use == for assigning a variable

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I have written this code to test something for some code I am writing and it only works if I use == rather than =:

#include <iostream>
using namespace std;
int main ()
{
int internal_organ_cream = 5;
int liquid_organs = 7;
&internal_organ_cream = &liquid_organs;
}

I tried running it like this but it didnt work but when I changed the = to a == it worked. I dont understand why because i thought == was for when you are checking not when you are assigning because here i am trying to make internal_organ_cream a reference of liquid_organs.

What I have tried:

nothing....................................................................

Posted 16-Mar-18 5:05am

BerthaDusStuf

Updated 16-Mar-18 5:11am

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OriginalGriff · Accepted Answer · 2018-03-16T05:12:00

Solution 1

It's because of the "&" in front of internal_organ_cream - remove them both and it will work:

C++

int internal_organ_cream = 5;
int liquid_organs = 7;
internal_organ_cream = liquid_organs;

When you put "&" in front of a variable name, it returns the address of the variable, rather than it's content - but that will be explained later when you get to pointers. For the moment, just don't use them at all!

Posted 16-Mar-18 5:12am

OriginalGriff

Comments

BerthaDusStuf 16-Mar-18 13:59pm

Hi thanks for your reply, yes i do know what the & does and i also have a fair bit of knoledge on pointers but i still dont know why there is a double equals there rather than single. is that something ill learn about or is there just a simple explanation for it? also i dont want to do it without the ampersand because i want it to have the same backing memory rather than make a copy

OriginalGriff 16-Mar-18 15:06pm

Please don't play with silly comments - you won't get near the maximum length, but you will annoy people whose browser width goes "all funny" as a result ... I delete it for you to prevent you getting tagged as a "abusive / trolling".

You don't need "==" to do the assignment - the reason it wanted it instead of a single "=" was that the & before the first variable changed it from an lvalue to an rvalue.
An lvalue can appear on the left of an assignment, and rvalue can't - the different being that an lvalue can be assigned to, or changed where an rvalue can't.
Lvalues are variables like "i", dereferenced pointers like "*pi", array elements like arr[10], and so forth.
Rvalues are constants like 666 , or calculated values line "i * 2". And the addresses of variables of course, like "&i".

When you added the ampersand, you changed "internal_organ_cream" from a lvalue to an rvalue, so the compiler assumed that you can mistyped the assignment "=" and intended a comparison "==" and gave you an appropriate error / warning message.

BerthaDusStuf 16-Mar-18 20:33pm

oh ok but then I tried running that program and it changed the value of it so it didnt compare, it actually assigned it that value

OriginalGriff 17-Mar-18 3:16am

Which is what you were wanting it to do ... wasn't it?

OriginalGriff 16-Mar-18 15:08pm

And the long message? That also annoy people who get a 4K line of "d"s delivered to their inbox ...