Why strlen() returns an unexpected value

Question

I wrote a program that gets a string (password) and checks its validity,
the conditions for the string are:

1. At least one number
2. At least one upper case and one lower case letter
3. Must contain 6 elements

So I covered the most of the conditions, but then I got troubled with the third condition, I tried using strlen() but it returned a wrong value.

Here is the code:

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

#define MAX 6
#define TRUE 1
#define FALSE 0

int passCheck(char password[]);

/*
main will ask the user to enter a password and then it will send it to 
passCheck, and check the return value, if the password is valid or not.
input: none
output: none
*/
int main()
{
    char password[MAX] = { 0 };
    printf("Enter a password: ");
    fgets(password, MAX, stdin);
    if(password[strlen(password)-1] = '\n') {password[strlen(password)-1] = 0;}
    if (passCheck(password) == TRUE)
    {
        printf("Valid");
    }
    else 
    {
        printf("Invalid");
    }
    return (0);
} 
/*
passCheck will take the password and will see if it's meeting the conditions
, then passCheck will return true(valid) or false(invalid).
input: password string
output: flag
*/
int passCheck(char password[])
{
    int i = 0;
    int flag = FALSE; // true(1) or false(0)
    int len = 0;
    int checkInt = 0; // checks if password has a digit
    int checkChar = 0;
    int copy = 0;

    for (i = 0; password[i]; i++)
    {   
        if (strlen(password) == MAX)
        {
            len = TRUE;
        }
        if (isdigit(password[i]))/*checks if the input is a number(0-9) or 
        a char (A-Z, a-z)
        */
        {       
            checkInt = TRUE;

        }
        if ((password[i] >= 'A' && password[i] <= 'Z') || (password[i] >= 'a' && password[i] <= 'z'))
        {
            checkChar = TRUE;
        }

        if (password[i] == password[i-1]) // checks if there is the same char/num in a row
        {
            copy = TRUE;
        }
        else
        {
            copy = FALSE;
        }
    }
    printf("%d %d %d %d\n" , len,checkInt, checkChar,strlen(password));
    if (copy)
    {
        flag = FALSE;
    }
    else if (len && checkInt && checkChar)
    {
        flag = TRUE;
    }
    return flag;
}

The printf() in the passCheck() function I used is for checking if the string meets the conditions, the output is working well, however len is not working and the strlen() function always returns 4 if the number is great than 4. Where did I go wrong?

Answer 1

#define MAX 6
char password[MAX] = { 0 }; // The LONGEST your password can be is 5-characters + NULL Terminator (\0)

strlen(password); // will never return anything more than 5.

If you want your password to be 6 characters, the buffer has to be 7-characters:

• 6 for the password
• 1 for the end-of-string marker: \\0