How many values is a function capable of returning?

namespace CuriousTabConsoleApplication
{ 
    class SampleProgram
    { 
        static void Main(string[] args)
        { 
            int[]arr = newint[]{ 1, 2, 3, 4, 5 }; 
            fun(ref arr);
        }
        static void fun(ref int[] a)
        { 
            for (int i = 0; i < a.Length; i++)
            { 
                a[i] = a[i] * 5; 
                Console.Write(a[ i ] + " "); 
            } 
        } 
    } 
}

namespace CuriousTabConsoleApplication
{
    class SampleProgram
    {
        static void Main(string[ ] args)
        {
            int i = 5;
            int j;
            fun1(ref i);
            fun2(out j);
            Console.WriteLine(i + ", " + j);
        }
        static void funl(ref int x)
        {
            x = x * x;
        }
        static void fun2(out int x)
        {
            x = 6; 
            x = x * x; 
        }
    }
}

1. Function definitions cannot be nested.
2. Functions can be called recursively.
3. If we do not return a value from a function then a value -1 gets returned.
4. To return the control from middle of a function exit function should be used.
5. Function calls can be nested.

fun(int i, Single j, double k) decimal 
{ ... }

static decimal fun(int i, Single j, double k) 
{ ... }

fun(int i, Single j, double k) 
{
    ...
    return decimal; 
}

static decimal fun(int i, Single j, double k) decimal 
{ ... }

1. A function cannot be called from a subroutine.
2. The ref keyword causes arguments to be passed by reference.
3. While using ref keyword any changes made to the parameter in the method will be reflected in that variable when control passes back to the calling method.
4. A subroutine cannot be called from a function.
5. Functions and subroutines can be called recursively.

1. C# allows a function to have arguments with default values.
2. C# allows a function to have variable number of arguments.
3. Omitting the return value type in method definition results into an exception.
4. Redefining a method parameter in the method's body causes an exception.
5. params is used to specify the syntax for a function with variable number of arguments.

namespace CuriousTabConsoleApplication
{
    class SampleProgram
    {
        static void Main(string[ ] args)
        {
            int i = 10;
            double d = 34.340;
            fun(i);
            fun(d);
        }
        static void fun(double d)
        {
            Console.WriteLine(d + " ");
        }
    }
}