An instance in a list is modified by a new one

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Hi all ! I'm kind of out of ideas so I need your help in this one.
it's hard to explain the situation but I'l try my best.

I have created a program that creates cars of some types and adds them to a Garage.
I represent the garage with a list. I put values to one instance and add it to the list, then I realize that when I start to add values to a new instance, it changes the values of the instance inside the list.

I'm confused Please help.

What I have tried:

don't really know what to try, I don't really know how it happened

Posted 27-Jan-17 17:14pm

Member 12971184

Updated 27-Jan-17 19:50pm

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Jon McKee 28-Jan-17 1:30am

Beyond Peter Leow's suggestion which is probably the issue you're having, could you post relevant code? Without seeing the code we can't point you to the exact area the code is modifying the pointer incorrectly.

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Peter Leow · Answer 1 · 2017-01-27T17:28:00

That is correct, the elements in the list are just references (pointers) to the actual car instances, this is called Passing Reference-Type Parameters (C# Programming Guide)[^]. Usually, we keep an actual artifact (by value) in a locker. For passing by reference, however, you keep information about the actual location (address) of that article on a piece of paper in that locker, this locker is the so-called pointer in C programming. To better grasp the concept, read out pointer[^].

Patrice T · Answer 2 · 2017-01-27T19:44:00

Quote:
I represent the garage with a list. I put values to one instance and add it to the list, then I realize that when I start to add values to a new instance, it changes the values of the instance inside the list.

Even without code, one can say is that what you think is 2 instances of 2 different things is in fact 2 pointers to same instance, thus the problem.

Along with deeper learning of programming techniques, you should learn debugger.

When you don't understand what your code is doing or why it does what it does, the answer is debugger.
Use the debugger to see what your code is doing. It allow you to execute lines 1 by 1 and to inspect variables as it execute, it is an incredible learning tool.

Debugger - Wikipedia, the free encyclopedia[^]
Mastering Debugging in Visual Studio 2010 - A Beginner's Guide[^]

The debugger is here to show you what your code is doing and your task is to compare with what it should do.
There is no magic in the debugger, it don't find bugs, it just help you to. When the code don't do what is expected, you are close to a bug.

An instance in a list is modified by a new one

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