int p = 3; // fixed length padding
int n = 55; // number to test

string t = n.ToString("D" + p); // magic     

Console.WriteLine("Hello, world! >> {0}", t);

// outputs: 
// Hello, world! >> 055

c# 6.0风格的字符串插值

int i = 1;
var str1 = $"{i:D4}";
var str2 = $"{i:0000}";

string hello = "Hello C# Corner.";

string helloHash = hello.PadLeft(5, '#');  

Console.WriteLine(helloHash); 

输出:

#####Hello C# Corner.

大多数给出的答案都很慢或很慢，或者对负数不适用。

试试这个:

}
    //
    //
    ///<summary>Format a value with a fixed number of digits.</summary>
    public static string Pad( this long v, int digits ) {
        int negative = 0;
        if ( v < 0 ) {
            negative = 1;
            v = Math.Abs( v );
        }
        var source = v.ToString();
        var length = source.Length;
        int max = length;
        if ( max < digits ) {
            max = digits;
        }
        max += negative;
        var ca = new char[ max ];
        for ( int i = 0; i < max; i++ ) {
            ca[ i ] = '0';
        }
        while ( length > 0 ) {
            ca[ --max ] = source[ --length ];
        }
        if ( 0 != negative ) ca[ 0 ] = '-';
        return new string( ca );
    }

i.ToString()。PadLeft(4， '0') -好的，但对负数无效 i.ToString(“0000”);-显式形式 i.ToString (D4);-简写格式说明符 ${: 0000}”;字符串插值(c# 6.0+)

int p = 3; // fixed length padding
int n = 55; // number to test

string t = n.ToString("D" + p); // magic     

Console.WriteLine("Hello, world! >> {0}", t);

// outputs: 
// Hello, world! >> 055