C# implements string class

 C# implements the String class. After the study, I have a deeper understanding of data structures and C#. Friends who are studying are welcome to discuss. QQ: 848367854

namespace _stringStudy
{
    class StringDS
    {
        private char[] data; //String array is used to store characters

        public StringDS(char[] array) //Construction
        {
            data = new char[array.Length];
            for(int i =0; i < data.Length; i++)
            {
                data[i] = array[i];
            }
        }
        public StringDS(string str) //construction
        { 
            data = new char[str.Length];
            for(int i=0; i< str.Length; i++)
            {
                data[i] = str[i];
            }
        }

        public char this[int index] //The indexer for accessing characters according to the index
        {
            get { return data[index]; }
        }

        public int GetLength() //The method to get the length of the string
        {
            return data.Length;
        }
        // / <summary>
        /// 1. If the current string is equal to s, return 0
        /// 2. If the current character is greater than s, return 1
        /// 3. If the current character is less than s, return -1
        /// 4. If The current string length is greater than the length of s, return 1, otherwise return -1
        /// </summary>
        /// <param name="s"></param>
        /// <returns></returns>
        public int Compare(StringDS s)
        {
            int index = -1; //index
            int len ​​= this.GetLength() < s.GetLength() ? this.GetLength() : s.GetLength();//Trinary operator, find the length of the string with the smallest length
            for (int i = 0; i < len; i++)
            {
                if (this[i] != s[i]) //As long as one character is different, assign the character index value to index
                {
                    index = i;
                    break ; //As soon as the difference is found, jump out of the loop immediately
                }              
            }
            if(index != -1) //The first len ​​length of the string finds different characters, and records the index value of different characters index
            {
                if (this[index]> s[index]) //If the value of the character at the index position of the current string is greater than the value of the index position of the s string, return 1
                {
                    return 1;
                }
                else //If the current string is at the index position The character value of the position is less than the value of the index position of the s string, return -1
                {
                    return -1;
                }
            }
            else //The first len ​​characters of the string are the same, and there are 3 cases
            {
                if(this.GetLength() = = s.GetLength()) // Case 1: The current string length is equal to the s string length, return 0
                {
                    return 0;
                }
                else
                {
                    if (this.GetLength() > s.GetLength()) // case 2: current string length is greater than s string, return 1
                    {
                        return 1;
                    }
                    else // case 3: current string length is less than s characters String, return -1
                    {
                        return -1;
                    }
                }
               

            }
        }
        public StringDS SubString(int index, int length)
        {
            char[] newChar = new char[length];
            for(int i = index; i < index + length; i++ )
            {
                newChar[i - index] = data[i];
            }
            return new StringDS(newChar);   
        }
        public StringDS Concat(StringDS s1,StringDS s2)
        {
            char[] newChar = new char[s1.GetLength() + s2.GetLength()];
            for(int i = 0; i < s1.GetLength(); i++)
            {
                newChar[i] = s1[i];
            }
            for(int i = s1.GetLength(); i < newChar.Length; i++)
            {
                newChar[i] = s2[i - s1.GetLength()];
            }
            return new StringDS(newChar);
        }
        public int IndexOf(StringDS s)
        {
            for(int i = 0; i <=this.GetLength() - s.GetLength();i++)
            {
                bool isEqual = true;
                for (int j = i; j < i + s.GetLength(); j++)
                {
                    if(this[j] != s[j - i])
                    {
                        isEqual = false;
                    }
                }
                if (isEqual)
                {
                    return i;
                }
                else
                {
                    continue;
                }
            }
            return -1;
        }

    }

}

namespace _stringStudy
{
    class Program
    {
        static void Main(string[] args)
        {
            char[] array = new char[] { 'A','B' ,'C'};
            Console.WriteLine(new StringDS(array).ToString());     //ABC


            StringDS s1 = new StringDS("abc");
            StringDS s2 = new StringDS("c");
            int j = s1.IndexOf(s2);
            Console.WriteLine(j);                                  //2
            
            StringDS s3 = new StringDS("I am a girl");
            Console.WriteLine(s3.ToString());                     //I am a girl


            StringDS s4 = new StringDS("the great");
            StringDS s5 = new StringDS(" wall");


            Console.WriteLine(s3.GetLength());                      //11
            Console.WriteLine(s4.GetLength());                      //9
            Console.WriteLine(s5.GetLength());                     // 4


            StringDS s6 = s3.SubString(7, 4);               
            Console.WriteLine(s6.ToString());                     //girl


            StringDS s7 = s4.SubString(3, 2);
            Console.WriteLine(s7.ToString());                     // g
           
            Console.WriteLine(StringDS.Concat(s4, s5).ToString());//the great wall


            Console.WriteLine(s4.Compare(new StringDS("the")));//1
            Console.WriteLine(s4.Compare(new StringDS("a")));//1
            Console.WriteLine(s4.Compare(new StringDS("z")));//-1
            Console.WriteLine(s4.Compare(new StringDS("the great")));//0
            Console.WriteLine(s5.Compare(new StringDS("     wall")));//0


            Console.WriteLine(s3.IndexOf(new StringDS("girl")));  //7
            Console.WriteLine(s4.IndexOf(new StringDS("the")));   //0
            Console.ReadKey();


        }
    }
}