C++ – How to check if a string is certain amount of characters and contains (or doesn’t contain) certain characters? C++

booleancerror handlinginputstring

Let's say I have two strings (string1, string2) based off of user inputs. I want string1 to be at least 5 characters, at most 10 characters, and only allowed to contain the following:

  1. Upper case letters
  2. Lower case letters
  3. Numbers (0-9)

Otherwise, the user will be prompted to keep entering strings until the requirements are met.

while(len(string1)<5 or len(string1)>10) {
    if(len(string1) > 10) {
        cout << "Please enter a string that is less than 10 characters: ";
        cin >> input;
    } else if(len(string) < 5) {
        cout << "Please enter a string that is more than 5 characters: ";
        cin >> input;
    } else {
        cout << "Please enter a string with legal characters (uppercase/lowercase letters and numbers): ";
        cin >> input;
    }

How would I check if string1 only contains uppercase letters, lowercase letters, and numbers? Would I use the following in some sort of way?…

string legalChars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";   
string1.find_first_not_of(legalChars)

As for string2, I want the user input to be at least 6 characters long and to contain at least one non-letter character. 

while(len(string2)<6) {
    if(len(string2)<6) {
        cout << "Please enter a string that is at least 6 characters long: ";
        cin >> input2;
    } 
}

How would I check for non-letter characters in string2? How should I approach this problem?

Best Answer

For string1 you can simply check for the length to be at least 5 characters and at most 10 characters (use std::string::length), and pass each character into isalnum to check if it is alphanumeric.

For string2 you can check that it's at least 6 characters long and has at least one uppercase letter by using isupper.

Or as @Lorehead pointed out, you can just use regex. Which is better is entirely up to you.

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