Validate string of letters and number

[SGTChubbz]

Hey guys, i'm running into trouble attempting to validate an user input string.

Basically they put in a variable length string of letters (a-z) and/or numbers (0-9). I'm attempting to go through the string and check if the inputs is valid (using isalnum(stringname[i])) but it will crash if it has multiple errors, or if there are invalid characters followed by valid ones. Also i was try to get it to where if it finds an error, it will prompt for another input string until the user enters a valid string...

string plaintext;
for (c=0;c<plaintext.size();c++)
            {
                if (isalnum(plaintext[c])
                    {
                    }
                else
                    {
                        cout <<"invalid character found in plaintext; Returning to Menu\n\n";
                        break;;
                    }
            }

[Hambone]

Maybe look into a lib that handles regular expressions?

[SGTChubbz]

What?

[JLBorges]

#include <iostream>
#include <string>
#include <cctype>

int main()
{
    std::string input ;
    
    while( input.empty() )
    {
        std::cout << "please type in a string consisting of only alphanumeric characters\n" ;
        std::cin >> input ;
        
        // validate
        for( char c : input ) // for each character in input
        {
            if( !std::isalnum(c) ) // if it is not alphanumeric
            {
                std::cout << "invalid character '" << c << "' found in input '" 
                          << input << "'. please try again\n" ;
                input.clear() ; // make input empty so that we go through the loop again
                break ;
            }
        }
    }
    
    std::cout << "validated input is: '" << input << "'\n" ;
}

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