Compare password to a given set of passwords

Question

I have got an assignment from uni which mentions that I have to compare a given set of passwords to the password given by the user. The set of passwords are predetermined in the question as follows

const char *passwd[NUM_PASSWDS] = {
    "123foo", "bar456", "bla_blubb"
};

and has to be compared with input from user...

So I have written my code as follows;

#include <stdio.h>
#include <string.h>

#define NUM_PASSWDS 3

const char *passwd[NUM_PASSWDS] = {
    "123foo", "bar456", "bla_blubb"
};

int pwdquery(char pass[]) {
    for (int i = 0; i < 2; i++) {
        if (passwd[i] == pass[i]) {
            return printf("correct");
        }
    }
}

int main() {
    char a[100];
    for (int i = 0; i < 3; i++) {
        printf("Please enter password");
        scanf("%s", a);
    }
    pwdquery(a);
}

When I tried running my code, it shows an error...

Thank you for your time

Answer 1

To compare string you need to strcmp function.
printf returns number of character printed. You should return fixed value on success or failure of password match. In my example I'm returning 1 in case of password match or 0 in case of no-password match.
In main function scanf function with %s argument can read entire string. You don't need for-loop to read input string.

#include<stdio.h>
#include<string.h>
#define NUM_PASSWDS 3

const char* passwd[NUM_PASSWDS] = {
"123foo", "bar456", "bla_blubb"
};
int pwdquery(char pass[]) {
    for (int i = 0; i < NUM_PASSWDS; i++) 
    {
        if (strcmp(pass, passwd[i]) == 0) 
        {
            return 1; // One means currect password
        }
    }
    return 0; // Zero means incorrect password password
}

int main() {
    char a[100];
    printf("Please enter password");
    scanf("%s", a);

    if(pwdquery(a) == 1)
    {
        printf("Password entered is correct");
    }
    else
    {
        printf("Password entered is incorrect");
    }
}

---

With custom strcmp

#include<stdio.h>
#include<string.h>
#define NUM_PASSWDS 3

const char* passwd[NUM_PASSWDS] = {
"123foo", "bar456", "bla_blubb"
};

//Returns 0 if string don't match else returns 1
int user_strcmp(const char *str1, const char *str2)
{
    size_t str1_size = strlen(str1);
    size_t str2_size = strlen(str2);
    if(str1_size != str2_size)
    {
        return 0; //String are not of same size. The strings won't match.
    }
    for(size_t i = 0; i < str1_size; i++)
    {
        if(str1[i] != str2[i])
        {
            return 0;
        }
    }
    return 1;
}
int pwdquery(char pass[]) {
    for (int i = 0; i < NUM_PASSWDS; i++) 
    {
        if (user_strcmp(pass, passwd[i]) == 1) 
        {
            return 1; // One means currect password
        }
    }
    return 0; // Zero means incorrect password password
}

int main() {
    char a[100];
    printf("Please enter password");
    scanf("%99s", a);

    if(pwdquery(a) == 1)
    {
        printf("Password entered is correct");
    }
    else
    {
        printf("Password entered is incorrect");
    }
}