string.cs

/// <summary>
/// 转全角(SBC case)
/// </summary>
/// <param name="input">任意字符串</param>
/// <returns>全角字符串</returns>
public static string ToSBC(this string input)
{
    char[] c = input.ToCharArray();
    for (int i = 0; i < c.Length; i++)
    {
        if (c[i] == 32)
        {
            c[i] = (char)12288;
            continue;
        }
        if (c[i] < 127)
            c[i] = (char)(c[i] + 65248);
    }
    return new string(c);
}

/// <summary>
/// 转半角(DBC case)
/// </summary>
/// <param name="input">任意字符串</param>
/// <returns>半角字符串</returns>
public static string ToDBC(this string input)
{
    char[] c = input.ToCharArray();
    for (int i = 0; i < c.Length; i++)
    {
        if (c[i] == 12288)
        {
            c[i] = (char)32;
            continue;
        }
        if (c[i] > 65280 && c[i] < 65375)
            c[i] = (char)(c[i] - 65248);
    }
    return new string(c);
}