Re-write the String class from the previous work, but use a singly-linked list of character as the representation. Like previous work, these strings...

Details are in the detail.docx.  Please upload a zip file with these files, String.h, String.cpp, test_main.cpp, standard_main.cpp.

Re-write the String class from the previous work, but use a singly-linked list of character as therepresentation. Like previous work, these strings will be of varying lengths and must grow and shrink asnecessary. Implement all the appropriate methods given below. Use memory storage proportional to thenumber of characters in the string (no more and no less). Any memory errors reported by valgrind willcause -40 points.● Write the static methods given below: copy(L), append(L1, L2), length(L), reverse(L), compare(L1, L2),stringToList(S), deleteList(L) This is the place to experiment with recursion. You could try writing themiteratively at first, then try recursion after you have the codes working.● Use the static methods to write the public methods as given in the class declaration below:● Class String declaration:class String{public:/// Both constructors should construct/// this String from the parameter sexplicit String( const char * s = "");String( const String & s );String operator = ( const String & s );char & operator ( const int index );int size() const;int indexOf( char c ) const;bool operator == ( const String & s ) const;bool operator < ( const String & s ) const;/// concatenates this and sString operator + ( const String & s ) const;/// concatenates s onto end of thisString operator += ( const String & s );String reverse() const; // does not modify this Stringvoid print( ostream & out ) const;void read( istream & in );~String();private:bool inBounds( int i ){return i >= 0 && i < length();}struct ListNode{char info;ListNode * next;ListNode(char newInfo, ListNode * newNext): info( newInfo ), next( newNext ){}// Below: primitives you *must* write and use (try recursion)static ListNode * stringToList(const char *s);static ListNode * copy(ListNode * L);static ListNode * reverse(ListNode * L, ListNode * R = 0);● staticstaticstaticstatic ListNode * append(ListNode * L1, ListNode * L2); // +int compare(ListNode * L1, ListNode * L2);//like strcmpvoid deleteList(ListNode * L);int length(ListNode * L); // O(N) so call rarely };ListNode * head; // no other data members!! - especially no len!};ostream & operator << ( ostream & out, String str );istream & operator >> ( istream & in, String & str );●●● Write a main function which tests each function defined in your class String.Make it work with the main we provided below.You must make sure your program works correctly with the test mains and that you have no memoryleaks. Be sure to run them under valgrind with appropriate arguments to show your programshave no memory leaks. //standard_main.cpp for project#include "String.h"int main(){String firstString("First");String secondString("Second");String thirdString(firstString);String fourthString("Fourth");String fifthString = String();cout << "+: " << firstString + secondString << endl;cout << "+=: " << (firstString += secondString) << endl;cout << "indexOf(char): " << firstString.indexOf('t') << endl;cout << "LT: " << (secondString < firstString) << endl;cout << "<<: "<< fifthString << endl;cout << "<<: "<< fourthString << endl;cout << "==: " << (fifthString == fourthString) << endl;cout << ": "<< thirdString[1] << endl;fifthString = thirdString;cout << "<<: " << fifthString << " " << thirdString << endl;cout << ": "<< fifthString[1] << endl;cout << ": "<< fifthString[10] << endl;cout << "Enter a test string: ";cin >> firstString;cout << firstString << endl;cout << (firstString < secondString) << endl;cout << (firstString == thirdString) << endl;return 0;}