How to assign a variable in one method and change/use it in another method?

Question

What changes do I have to make for the x and z variables to retain the values they are assigned in the Assign method? I have only recently started learning C# for college after learning C++ for 2 years in school so this is very confusing to me.

class Program
{
    static void Assign(int x, int z)
    {
        x = 3;
        z = 2;
    }

    static void Sum(int x, int z)
    {
        Console.WriteLine(x + z);
    }

    static void Main(string[] args)
    {   
        int x = 0, z = 0;
        Assign(x,z);
        Sum(x,z);
    }
}

Surely they covered variable scope or passing arguments, no? Please read [ask] and take the [tour] — Ňɏssa Pøngjǣrdenlarp, Sep 21 '17 at 16:18
You could declare them in a higher scope or pass them by ref. — Equalsk, Sep 21 '17 at 16:18
What would you do in C++? You'd make them private member variables. But in C# you'd call them fields. What were you doing in C++ for those two years you spent learning it? — 15ee8f99-57ff-4f92-890c-b56153, Sep 21 '17 at 16:18
Possible duplicate of [C# referencing a variable from another method](https://stackoverflow.com/questions/9301197/c-sharp-referencing-a-variable-from-another-method) (and countless others) — Ňɏssa Pøngjǣrdenlarp, Sep 21 '17 at 16:26
The only things we were shown about C# were console input/output, if statements and for/while loops in the first lecture. — Rink prog, Sep 21 '17 at 16:27
Another option is top use tuple deconstruction in c# 7.0: `static (int, int) Assign() { return (3, 2); }` Then in the calling code: `(int x, int y) = Assign();` — Chris Dunaway, Sep 21 '17 at 17:52

sdgfsdh · Accepted Answer · 2017-09-21T16:26:04.920

2

You seem to have misunderstood how variable scopes work. The x in Assign is not the same as x in Main. This is because in C#, int is passed by value (this is the same as C++, BTW).

You probably meant to mark the variables in Assign as ref:

class Program
{
    static void Assign(ref int x, ref int z)
    {
        x = 3;
        z = 2;
    }

    static void Sum(int x, int z)
    {
        Console.WriteLine(x + z);
    }

    static void Main(string[] args)
    {   
        int x = 0, z = 0;
        Assign(x, z);
        Sum(x, z);
    }
}

Note the this is not recommended, because now Assign has side-effects. This is better:

class Program
{
    static void PrintSum(int x, int z)
    {
        Console.WriteLine(x + z);
    }

    static void Main(string[] args)
    {   
        PrintSum(3, 2);
    }
}

For more background, I would suggest looking at the difference between pass-by-reference and pass-by-value.

edited Sep 21 '17 at 16:26

answered Sep 21 '17 at 16:22

sdgfsdh

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+1 but I don't think the OP "probably" meant to use ref at all, they are just a confused beginner; your second example is the only one that makes sense. – Polyfun Sep 21 '17 at 16:25
To me, this question looks like homework about reference-vs-value, so I answered it that way. – sdgfsdh Sep 21 '17 at 16:26
Another option is top use tuple deconstruction in c# 7.0: `static (int, int) Assign() { return (3, 2); }` Then in the calling code: `(int x, int y) = Assign();` – Chris Dunaway Sep 21 '17 at 17:52

How to assign a variable in one method and change/use it in another method?

1 Answers1