firstly i would ask what is the purpose of your code, what are you trying to accomplish?
cin is an object of class ifstream, basically it accepts input from an external source such as your keyboard.
Here is an example:
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#include<iostream> //header that includes stream objects eg cin and cout
int main()
{ string name;
cout<<"What is your name?";//sends question to screen asking user for name
cin>>name;//allows the user to enter name and stores what was entered to
return 0;
}