Mutable--keyword

Arrays/Heap.cpp

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+//there is no way of knowing the size of array in c++;but there is a way cause when you delete this heap memory compiler needs to know the size of array but its comprimising
+
+#include <iostream>
+#include <array>
+
+class Entity
+{
+    public :
+
+      static const int exampleSize = 5;//constexpr will explained later which is constant expression
+      int* example[exampleSize];//suppose we changed it to a heap we first get the Entity memory adress which leads to the array  its a jumping across the memory so [better to switch it to stack]
+
+    std::array<int, 5> another;//type and size
+
+      Entity()
+      {
+
+
+         int a[5];
+
+        int count =  sizeof(a) / sizeof(int);//size means bytes ,count means no of elements 
+
+        //example->size();//we cant do like this like some other languages for heap in Entity class
+           for(int i = 0; i < another.size(); i++)
+             example[i] = 2;//constructor which initializes
+
+      }
+};
+
+int main()
+{
+
+    Entity e;
+
+    /*int example[5];
+    for(int i = 0; i < 5; i++)
+    example[i] = 2;*///we moved into the Entity class
+
+
+    //int* another = new int[5];
+    //for(int i = 0; i < 5; i++)
+    //another[i] = 2;
+
+
+    //delete[] another;
+
+
+    std::cin.get();
+}
+//this is based on heap allocated memory with new keyword
+//we  need to manually delete this
+//stack created it will ends when we get out of curly bracket int example[5]
+//heap created more over the stack cause of the life times most probably suppose if we need to return the array inside of our funtion
+
+//in c++ 11 there is called standard array which has inbuilt datastructures  used rather than the normal raw array
+//it includes bounds checking and it keeps tracking size of arrray

Arrays/Log.cpp

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+#include <iostream>
+
+int main()
+{ 
+    int example[5];
+    int* ptr = example;
+
+
+    for (int i = 0; i < 5; i++)
+            //example[i] = 2;//this is a text an offset to this memory of array
+
+
+
+     example[2] = 5;//for index 2 its start at 9th byte we are writting an offset of 8 bytes from a pointer
+    *(ptr + 2) = 6;//we are dereferencing this pointer way of writting and changing value from 5 to 6
+    *(int*)((char*)ptr + 8) = 6;//this is the way of writting in single bit[char] and even in int data type of 4 bytes
+
+
+    std::cin.get();
+}
+
+//arrays are always stored in rows ; each integer of 4 bytes total 20 bytes;
+//array is just a pointer here it is a int pointer

Arrays/main.cpp

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+//in java we have no modifier = default modifier
+//in c# we have such as internal[these are topics in visibility]
+/*Arrays in C++ are a collection of multiple elements of the same type stored in contiguous memory locations (one after another).[in rows]
+They are one of the most basic and important data structures in C++.*/
+//lua language starts from index 1;c++ is 0 
+//its like having multiple variables in a single variable
+//arrays mostly work with for loops[indexable loops];without it we need to set manually the example array
+
+#include <iostream>
+
+int main()
+{
+    int example[5]; //array type and name mentioned its contain 5 integers
+    example[0] = 2;
+    example[4] = 4;//last index
+
+    example[-1] = 5;
+    example[17] = 21;//we get memory access violation [in debug mode we get errors not in release mode]
+
+
+    std::cout << example[0] << std::endl;//with mentioning index, we get underlying data type
+    std::cout << example << std::endl;//actual array print memory adress cause its a pointer type
+
+
+
+    std::cin.get();
+}

Interfaces/main.cpp

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+/*Pure virtual function in C++ is the key feature that lets you create interfaces (or abstract classes that behave like interfaces).
+What is a Pure Virtual Function?
+A pure virtual function is a virtual function that:
+
+Has = 0 at the end
+Has no implementation in the base class (or sometimes just a dummy one)
+Forces every derived (child) class to provide its own implementation
+we cant instantiate the interface class [only sub classes we can and have to]
+Interfaces are just classes in c++ with unimplemented methods acting as template of source unlike other languages as java or c#*/
+
+
+#include <iostream>
+#include <string>
+
+  class Printable
+
+    {
+  public :
+     virtual std::string GetClassName() = 0;//now every class have to contain GetClassName function to implement
+
+    };
+
+      class Entity : public Printable//made a sub class
+    {
+        public :
+          virtual std::string GetName() { return "Entity"; }//by removing body and equating to 0 makes a pure virtal funtion
+          std::string GetClassName() override { return "Entity"; } 
+
+        };
+
+    class Player : public Entity //no need of printable 
+    {
+        private :
+          std::string m_Name;
+      public :
+          Player(const std::string& name)
+               : m_Name(name) {}
+
+               std::string GetName() override { return m_Name; }
+               std::string GetClassName() override { return "Player"; } 
+    };
+
+    void PrintName(Entity* entity)
+    {
+          std::cout << entity->GetName() << std::endl;
+    }
+
+    class A : public Printable 
+    {
+       public :
+           std::string GetClassName() override {return "A"; }
+
+    };
+
+
+    void Print(Printable* obj)//this is for printing names of class and type which has GetClassName funtion and make Printable a pointer 
+{
+    std::cout << obj->GetClassName() << std::endl;
+}
+int main()
+{
+
+    Entity* e = new Entity();//cant instantiate the Entity class if it is pure virtual funtion and we need to give a sub class where the funtion is implemented eg Player("")
+   // PrintName(e);
+
+
+    Player* p = new Player("Suhas");
+    //PrintName(p);
+
+    Print(e);
+    Print(p);
+    Print(new A());//it is a memory leak
+
+
+
+    std::cin.get();
+}
+    //we can only instantiate the class if it actually has all those pure virtual functions implemented[all funtions implemented]

Mutable--keyword/Lambda.cpp

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+#include <iostream>
+#include <string>
+
+class Entity
+{
+  private :
+          std::string m_Name;
+          mutable int m_DebugCount = 0;
+
+   public :
+       const std::string& GetName() const
+       {
+        m_DebugCount++;
+        return m_Name;
+       }
+
+};
+
+int main()
+{
+
+    class Entity e ;
+    e.GetName();
+
+    int x = 8;
+    auto f = [=]() mutable
+                        //we can write &x or x or = or &
+    {
+        //std::cout << "Hello" << std::endl;
+        //x++;//by value = we get error we need to get it through local variable so better to use mutable keyword
+
+        /*  int y = x;
+          y++;
+        std::cout << y << std::endl;*/
+
+        x++;//we passed it through value through mutable keyword
+        std::cout << x << std::endl;
+
+    };
+
+    f();
+             //x = 8 cause we pased through value than reference
+    std::cin.get();
+}
+        /*lambda is a little through away funtion 
+               you can write and
+        assign it to the variable quickly */

Mutable--keyword/main.cpp

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+/*the application of mutable mostly with lambdas and const
+   its like mutable reversing the meaning of const*/
+
+#include <iostream>
+#include <string>
+
+class Entity
+{
+  private :
+          std::string m_Name;
+          mutable int m_DebugCount = 0;
+
+   public :
+       const std::string& GetName() const//const and ref
+           //making methods const so not to modify the class
+
+       {
+        m_DebugCount++;//its for supppose how many times we debugging
+        return m_Name;
+       }
+
+};
+
+int main()
+{
+
+    class Entity e ;
+    e.GetName();//we will do if the method is const
+
+    std::cin.get();
+}

String - Literals/Log.cpp

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+#include <iostream>
+#include <string>
+
+#include <stdlib.h>
+
+int main()
+{
+
+    using namespace std::string_literals;//gives no of funtions for convenience
+
+    std::string name0 = std::string("Cherno") + "hello!";//cant do cause you cant add 2 raw literals directly 
+    std::string name0 = "Cherno"s + "hello!";//this s returns a standard string and u8 for normal string and L infront of the string literals for wide string
+
+
+    std::u32string name0 = U"Cherno"s + U" hello";//for wide string it is wstring and R for row
+
+    const char* example = R"(Line1
+    Line2
+    Line3
+    Line4)";
+
+      const char* ex = "Line1\n"
+           "Line2\n"
+            "Line3\n";           
+
+
+
+    const char* name = u8"Cherno";//made with utf 8 similar to remaining ones [ unicode transformation format ]
+    const wchar_t* name2 = L"Cherno";//wide and this is 2 bytes per character[but variable for such as linux and windows]
+
+    const char16_t* name3 = u"Cherno";//2 bytes per character or 16 bits a character using string
+    const char32_t* name4 = U"Cherno";//32 bits character or 4 bytes per character
+
+
+
+    std::cin.get();
+}
+
+/*string literals are always stored in read only memory
+       so i cant equate a char pointer to a string litreral 
+         which is a READ ONLY MEMORY
+         we can use a const char array */ 

String - Literals/main.cpp

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+#include <iostream>
+#include <string>
+
+#include <stdlib.h>
+#include <cstring>
+
+        /*just a standard c library include 3 funtions and 
+               its a string literal also written as
+                    "Suhas"; 0[this is numeric zero]*/
+
+int main()
+{
+    const char name[8] = "Che\0rno";
+
+              /*8 cause it even ends with \0*/
+
+    std::cout << strlen(name) << std::endl;
+
+    std::cin.get();
+}

Strings - working/Log.cpp

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+#include <iostream>
+#include <string>
+
+void PrintString(const std::string& string)//creating copy of that std::string class
+
+{
+   // string += "h"; by removing the const and the refernce keywords and its just a read only function
+    std::cout << string << std::endl;
+
+}
+
+int main()
+{
+     std::string name = "Suhas";// + "hello!";process of appending strings
+     name += "hello!";
+
+     std::string name = std::string("Suhas") + "hello";
+     PrintString(name);
+     bool contains = name.find("no") != std::string::npos;//to find text in our string
+
+       /*npos is the illegal position for that find
+       and name.find returns position of that no thing*/
+
+
+     name.size();
+
+            /*strlen(s) for the length of the string char* s
+                and strcpy for copying of the strings*/
+
+
+
+     std::cout << name << std::endl;
+
+     std::cin.get();
+
+}          /* string copying in funtions are quite slow
+        strings can be addable than char ptrs  */