How to read a string character by character

[iamyiyaj]

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.

//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;
}

[SECMoG1T]

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

[iamyiyaj]

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.

[SECMoG1T]

you tell if it is valid by checking if the input conforms to the rules usually by using conditions

#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;
}

[Enoizat]

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?