Thread: Beginner question - dealing with blank non-null characters

Hey guys, just starting to learn C, and have a question.
I'm going through this tutorial series: https://www.youtube.com/watch?v=PVTD...6nhGJ9Vlcjyymq

And the first 'challenge' given by the presenter is giving me problems. Here's the code:

Code:

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <string.h>
#include <math.h>

int main(){
    char userPassword[30];
    printf("Enter a password: ");
    scanf(" %s", userPassword);
    char blank[1];

    int trueA, trueB, trueC;
    trueA = trueB = trueC = 0;
    int passLoop = 0;
    while (passLoop != 31) {
        if ((isalpha(userPassword[passLoop]) == 1)&&(isupper(userPassword[passLoop]) == 1)){printf("ALPHA!"); trueA = 1;}
        if (isdigit(userPassword[passLoop]) == 1) {printf("DIGIT!"); trueB = 1;}
        if ((isascii(userPassword[passLoop]) == 1)&&(isgraph(userPassword[passLoop]))&&(ispunct(userPassword[passLoop]))) {printf("ASCII!"); trueC = 1;}
        passLoop++;
    }
    if ((trueA == 1)&&(trueB == 1)&&(trueC == 1)) {printf("Password accepted!");}
    else {printf("Password cannot be used!");}

    return 0;
    }

The user is supposed to input a password that contains at least one upper case letter, one number, and one symbol. If it contains all three of those things it returns "Password accepted!", if not it returns "Password cannot be used!". The problem is with the symbol part, as I have absolutely no idea how to determine which characters in the array have been left unused. As a result it always returns false positives.

Can any of you experienced C coders explain to me what the correct way to deal with this is?

isspace() is the correct function to use. It returns true for any white space character. Be aware that using %s in scanf() means that the password won't contain white space though, so it is a pointless test. scanf() will actually stop reading a string for %s after it finds white space.

Edit: Oh, it seems like your question has changed - or maybe I read it wrong in the first place. Well, it depends on what you want to call a symbol. To me, at least, it is a non-alpha-numeric character.

Code:

if (!isalnum(userPassword[passLoop]))

The question is, is this good enough? I played the video, it seemed like he wanted something to match '$' only. Perhaps you are expanding it, but a direct comparison would suffice.

Originally Posted by MrHobbyBot

Code:

        if ((isalpha(userPassword[passLoop]) == 1) ...

Don't perform tests like this using == 1. Using the 'is' functions should be done like this:

Code:

    if (isalpha(ch)) 
        /* do something */

The reason is that isalpha and most other functions returning a yes/no answer are allowed to return any nonzero value to represent "yes". Testing against 1 in particular may work sometimes but it is not correct. Your test might fail when you least expect it because one of those functions decided to return, say, 53 or -128 instead of 1.

If, else if... is perfect for this

Code:

testresult =0; i=strlen(password);
while(i--){
if (password[i] >= 'a' && password[i] =< 'z') testresult |= 1;
else if (password[i] >= 'A' && password[i] =< 'Z') testresult |= 2;
else if (password[i] >= '0' && password[i] =< '9') testresult |= 4;
else if (password[i] >= '!' && password[i] =< '/') testresult |= 8;
}
if (testresult == 15)  OK code;

NOT tested and some special char are not included