如何在不使用库函数的情况下在C＃中将Int转换为String？

Question

What is the most effective code to convert int to string without using a native convert function.

 public static void Main(string[] args)
    {
        string y = Convert(990);
        Console.WriteLine(y);
        Console.ReadLine(); 
    }


    public static string Convert(int x)
    {

         char[] Str = new char[20];
         int i = 0;
         while (x != 0)
         {
             Str[i++] = x % 10 + '0';
             x = x / 10;
         }

         return Str.ToString();// How do I handle this without the native function?
    }

The above doesnt seem to work. Please advise.

Answer 1

You are adding the least significant digits to the start of the string. You'll need to reverse the string, or add the digits in reverse order, or insert them rather than append them.

And you'll need to do some casting. For example, here's one way to do it:

Str[i++] = (char)(x % 10 + '0');

Finally, you cannot use ToString() like that. You want this:

return new string(Str, 0, i);

Although StringBuilder might be more suitable.

And note that your code won't work properly for negative input values, or for zero.

So, here's a version that handles all of that:

public static string Convert(int x)
{
    if (x == 0)
    {
        return "0";
    }
    StringBuilder sb = new StringBuilder();
    string prefix = "";
    if (x < 0)
    {
        prefix = "-";
        x = -x;
    }
    while (x != 0)
    {
        sb.Insert(0, (char)(x % 10 + '0'));
        x = x / 10;
    }
    return prefix + sb.ToString();
}

This is pretty ugly though!

Answer 2

It might be easier to construct your result using a StringBuilder rather than a char array:

public static string Convert(int x)
{
     StringBuilder sb = new StringBuilder();

     while (x != 0)
     {
         sb.Insert(0, (char)(x % 10 + '0'));
         x = x / 10;
     }

     return sb.ToString();
}

The Insert(0, x) allows you to insert the more significant digits at the front.

Answer 3

Here's a solution without a String constructor or a .ToString() call. This one handles negative numbers. It's a bit too 'clever' for my taste, but it's an academic exercise anyway...

void Main()
{
    Console.WriteLine(Convert(-5432));
}

String Convert(int i)
{
    return String.Join("",Digits(i).Reverse());
}

IEnumerable<char> Digits(int i)
{
    bool neg = false;
    if(i==0) {yield return '0'; yield break;}
    if(i<0) { i = -i; neg = true;}
    while (i!=0)
    {
        char digit = (char)(i % 10 + '0');
        i = i / 10;
        yield return digit;
    }
    if(neg) yield return '-';

    yield break;
}