Lambda function using a delegate

Question

I have the following:

class Program {

    delegate int myDelegate(int x);

    static void Main(string[] args) {

        Program p = new Program();
        Console.WriteLine(p.writeOutput(3, new myDelegate(x => x*x)));

        Console.WriteLine("press [enter] to exit");
        Console.ReadLine();
    }
    private string writeOutput(int x, myDelegate del) {
        return string.Format("{0}^2 = {1}",x, del(x));
    }
}

Is the method writeOutput in the above required? Can the following be re-written, without writeoutput, to output the same as the above?

Can the line Console.WriteLine("x^2 = {0}", new myDelegate(x => x*x)); be amended so that 3 is fed into the function?

class Program {

    delegate int myDelegate(int x);

    static void Main(string[] args) {

        Program p = new Program();

        Console.WriteLine("x^2 = {0}", new myDelegate(x => x*x));

        Console.WriteLine("press [enter] to exit");
        Console.ReadLine();
    }
}

Unless you're practicing the use of delegates, I don't see why it would be necessary in your code. You have the value, and you know what to do with it. — Androiderson
– Androiderson, Commented Feb 3, 2013 at 13:49
@AndersonSilva - right the first time - I'm sand-pitting delegates and lambda functions — whytheq
– whytheq, Commented Feb 4, 2013 at 8:16

Zlatomir · Accepted Answer · 2013-02-03 13:37:39Z

1

It obviously can't be written that way. Think about this: what value x has in the second code? you create an instance of your delegate, but when it is called?

Use this code:

myDelegate myDelegateInstance = new myDelegate(x => x * x);
Console.WriteLine("x^2 = {0}", myDelegateInstance(3));

answered Feb 3, 2013 at 13:37

Zlatomir

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Comments

Petar Ivanov · Accepted Answer · 2013-02-03 13:38:47Z

1

You fon't really need a delagate. But in order to work you need to change this line:

    Console.WriteLine("x^2 = {0}", new myDelegate(x => x*x));

with this:

    Console.WriteLine("{0}^2 = {1}", x, x*x);

answered Feb 3, 2013 at 13:38

Petar Ivanov

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1 Comment

whytheq Over a year ago

+1 thanks Petar - but the point of the exercise is that I'm trying to understand delegates and how lambdas relate to them

antonijn · Accepted Answer · 2013-02-03 16:24:55Z

1

Firstly, you don't need a delegate. You can just multiply it directly. But first, the correction of the delegate.

myDelegate instance = x => x * x;
Console.WriteLine("x^2 = {0}", instance(3));

You should treat every instance of a delegate like a function, in the same way you do it in the first example. The new myDelegate(/* blah blah */) is not necessary. You can use a lambda directly.

I assume you're practicing the use of delegates/lambdas, because you could just have written this:

Console.WriteLine("x^2 = {0}", 3 * 3);

answered Feb 3, 2013 at 16:24

antonijn

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1 Comment

whytheq Over a year ago

+1 exactly - just practicing delegates/lambda and trying to get my head around how they work

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