How to read a string character by character

I have to write a program using a while loop to read a string that represents an identifier character by character. I know how to do while loops but that is all im challenged with. I would love explanations as i would love to learn this stuff and get better with it. Thanks in advance.
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//Enter an identifier and identify if it is
//a valid C++ identifier and follows the rules of C++ identifiers
#include <iostream>
#include <string>
using namespace std;
int main()
{
	string identifier;
	cout << " Please enter a C++ identifier and press enter immediately after." << endl;
	cin >> identifier;
	
	cin.get();
	return 0;
}
here are some of the rules , you can use an if statement to check if they are met


The rules of naming identifiers in C++ :
-----------------------------------------------

1. C++ is case-sensitive so that Uppercase Letters and Lower Case letters are different

2. The name of identifier cannot begin with a digit. However, Underscore can be used as first  
    character while declaring the identifier.

3. Only alphabetic characters, digits and underscore (_) are permitted in C++ language for 
     declaring identifier. Other special characters are not allowed for naming a variable / 
     identifier

4. Keywords cannot be used as Identifier.


How to read a string character by character?
use a loop and an index to access the string just like in arrays, or you could use a range based for loop that will automatically do the indexing for you.



references
http://www.c4learn.com/cplusplus/cpp-identifiers-tokens/
https://www.thoughtco.com/definition-of-identifier-958092
http://en.cppreference.com/w/cpp/language/identifiers
Last edited on
Thanks for the rules i know of those but i am not sure of how to make it into a code. For example the output would have my cout statement above and then i would enter an identifier and within seeing it it would tell if it is a valid identifier or not. For example if i enter _3digitone in the cin operator, the statement would be that this isn't valid.
you tell if it is valid by checking if the input conforms to the rules usually by using conditions

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#include <iostream>
#include <string>
using namespace std;
int main()
{
	string identifier;
	cout << " Please enter a C++ identifier and press enter immediately after." << endl;
	cin >> identifier;
	
        bool isvalid = true;
        ///check for conformity here
        if(identifier conforms to rule one)
          //do nothing
        else
          //is not valid isvalid = false;
      
       ///check all other rules
      //lastly
        if(isvalid)
          //print identifier valid
        else// print erro
	cin.get();
	return 0;
}
You could try with a logic like this:
- if in your string you find something which is not a letter or a digit, than the identifier is bad (suggestion: std::string::find_first_not_of() )
http://en.cppreference.com/w/cpp/string/basic_string/find_first_not_of
- if the first character is not a letter or an underscore, than the identifier is bad.
Are there further checks needed?
Do you need the code?
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