Validation of password input in C [closed] - c

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I have no idea how to go further with this program that I'm about to create. This is the idea:
Validate the password input to check if the password has at least one
uppercase letter, lowercase letter and a number.
Some parts of it is broken at the moment. For instance the false, true statements. And the "undynamic" char array in the main function. I don't know how to make that at the moment either. But it explains what I'm looking for.
So how can I validate this without writing too much code?
This is my current code:
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
int passval(char pw[])
{
int x;
for (x = 0; x < sizeof(pw); x++) {
if ( (isalnum(pw[x])) || (ispunct(pw[x])) ) {
return 0;
} else {
return 1;
}
}
return 0;
}
int main()
{
char password[20];
printf("Enter password: ");
scanf("%s", password);
if (passval(password) == TRUE) {
printf("Password is TRUE");
}
return 0;
}

Answer 1

#include <stdio.h>
#include <string.h>
#include <ctype.h>
int
password_validate(const char *pass)
{
int upper = 0, lower = 0, digit = 0;
if (pass == NULL || strlen(pass) == 0)
return -1;
do
{
if (isupper(*pass))
upper = 1;
if (islower(*pass))
lower = 1;
if (isdigit(*pass))
digit = 1;
} while ((!lower || !upper || !digit) && *(++pass));
return (*pass != '\0' ? 0 : (upper == 0 ? -2 : (lower == 0 ? -3 : -4)));
}
Please view the below link to a code sample to be sure to understand some of the corner cases (thank you Alex Pogue for highlighting additional cases) and how this function handles them.
https://ideone.com/GiOGkj

Answer 2

Scan for the string.
If the characters to be found exists, raise flags.
Say "valid" iff all of the required flags are raised.
Example implementation:
#include <ctype.h>
int passval(const char pw[])
{
size_t x;
unsigned char c; /* making this unsigned is important:
char may be negative and passing it to isupper(), etc. may invoke undefined behavior */
int upperExists = 0, lowerExists = 0, numberExists = 0;
for (x = 0; pw[x] != '\0'; x++) {
/* fetch the character */
c = pw[x];
/* raise flags when the character is required kind */
upperExists = upperExists || isupper(c);
lowerExists = lowerExists || islower(c);
numberExists = numberExists || isdigit(c);
}
/* check if all of required flags are raised */
return upperExists && lowerExists && numberExists;
}

Answer 3

Arrays that are passed to a function decay into pointers so you cannot do sizeof() in your function, instead pass the string length strlen()
I would do something like this
#include <ctype.h>
#include <stdbool.h>
bool validatePassword(const char* pw, const int len)
{
int x;
bool upperCase = false;
bool lowerCase = false;
bool number = false;
for (x = 0; x < len; x++)
{
if ( pw[x] == toupper(pw[x]) )
{
upperCase = true;
}
else if ( pw[x] == tolower(pw[x]) )
{
lowerCase = true;
}
else if ( isdigit(pw[x]) )
{
number = true;
}
}
return upperCase && lowerCase && number;
}

Answer 4

My solution is based on parsing a string that ends with a \0 character, check for at least one capital char, small char, and a digit like how an OR gate functions..
Try Online
int passval(char * p)
{
int capital=0, small=0, digit=0;
while (*p && !(capital && small && digit))
capital = (*p>='A' && *p<='Z' ? 1 : capital),
small = (*p>='a' && *p<='z' ? 1 : small ),
digit = (*p>='0' && *p<='9' ? 1 : digit ),
p++ ;
return capital && small && digit;
}