Using auto specified we can declare any variable without specifying it’s data type. Variable will automatically determine it’s data type using value assign to variable.

  auto Int_Var = 1;
  auto Char_Var = 'P';
  auto Str_Var = "Hello";
  
  cout<< Int_Var <<endl;  // Output Integer value: 1
  cout<< Char_Var <<endl; // Output Character value: P
  cout<< Str_Var <<endl;  // Output String value: Hello

We can also store Lambda function inside auto variable.

#include <iostream>
using namespace std;

auto AddFunc = [](int a, int b)
{
    return (a + b);
}; 

int main()
{
  cout << AddFunc(1,2) << endl;  // output : 3
  return 0;
}

Main advantage of auto comes with types that are long to write.

#include<iostream>
#include<map>
using namespace std;
int main()
{
 map<int,string> MapObj;
 MapObj.insert(pair<int,string>(1,"One"));
 MapObj.insert(pair<int,string>(2,"Two"));
 MapObj.insert(pair<int,string>(3,"Three"));

 //map<int,string>::iterator it = MapObj.begin();
 auto it = MapObj.begin(); // benefit or auto
 
 while(it != MapObj.end()){
     cout<<it->first<<"::"<<it->second<<endl;
     it++;
 }
  return 0;
}

Once we have initialized the auto variable then you can change the value but you cannot change the type.

  auto MyVar = 10;
  cout<<MyVar<<endl;
  
  MyVar = 20;
  cout<<MyVar<<endl;
  
  MyVar = "HELLO";
  //error: invalid conversion from ‘const char*’ to ‘int’

auto cannot be left uninitialized. We must initialize it with value.

  auto MyVar;
  //error: declaration of ‘auto MyVar’ has no initializer

In C++11, you can now put the return value at the end of the function declaration, substituting auto for the name of the return type.

auto Add(int a, int b) -> int
{
    return (a+b);
}

int main()
{
  auto MyVar = Add(1,2);
  cout<<MyVar<<endl; // Output: 3
  return 0;
}