如何设置哪些功能输入是必需的，哪些不需要（C＃）

Question

So I have a function

public int Sum(var valueA, var valueB, var valueC) { 
  var summ = valueA + valueB; 
  return summ; 
} 

I want to add to summ valueC if it was given. And let user not specify it if he does not want to. How to do such thing?

Answer 1

You can do this in C# 4.0 with optional arguments . If you're using a version prior to C# 4.0, you could create an overloaded function that calls your function with a default value.

Answer 2

If you are using .NET 3.5 or earlier you can use Nullable Types .

public int Sum(int valueA, int valueB, int? valueC)
{
    int sum = valueA + valueB;
    if (valueC.HasValue)
    {
        sum += valueC.Value;
    }

    return sum;
}

The calls would be:

int answer1 = Sum(1, 2, 3); // = 6

int answer2 = Sum(1, 2, null); // = 3

Of course the classic way to do this is to use method overloads:

public int Sum(int valueA, int valueB)
{
    int sum = valueA + valueB;
    return sum;
}

public int Sum(int valueA, int valueB, int valueC)
{
    int sum = valueA + valueB + valueC;
    return sum;
}

int answer1 = Sum(1, 2);
int answer2 = Sum(1, 2, 3);

If you want to be able to use string as well as int either move to .NET4 or create another pair of overloaded methods:

public int Sum(string valueA, string valueB)
{
    // Convert the strings to int and call the previous code
    // You will need to cope with the case when the strings don't represent numbers
}

public int Sum(string valueA, string valueB, string valueC)
{
    ...
}

If you want to cope with mixed string and int then you'll need even more overloads - which is probably overkill.

Answer 3

In addition to the options that Shane Fulmer provided, you can also use the params keyword to have a function that takes a variable number of parameters:

public int Sum(params int[] values)
{
    int sum = 0;
    for(int i = 0; i < values.Length; i++){
        sum+=values[i];
    }
    return sum;
}

int answer2Parameters = Sum(1, 5);
int answer3Parameters = Sum(1, 2, 3);
int answer4Parameters = Sum(1, 3, 5, 6);

Of course if you want to limit them to exactly two or three then you probably want to look at optional parameters in C#4.0 or overload the Sum function - by this I mean create two Sum functions, one that takes two parameters and another that takes 3 parameters.

public int Sum(int valueA, int valueB) { 
  int summ = valueA + valueB; 
  return summ; 
} 

public int Sum(int valueA, int valueB, int valueC) { 
  int summ = valueA + valueB + valueC; 
  return summ; 
}