advent of code day 4 C

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

#include <time.h>

clock_t start, end;
double cpu_time_used;
//static int cmp(const void *a, const void *b) { return *(char *)a - *(char *)b; }
// for pt2

int main(void)
{
    start = clock();
    // open in the password file and check for errors
    FILE *fp;
    fp = fopen("pass.txt", "r");
    if(fp == NULL)
    {
        printf("Failed to open password file\n");
        exit(1); // exit with error if file not found
    }
    char string[100]; // string to read line in
    char *tokenPtr; // pointer to token
    char **arr; // pointer to array of strings
    int i = 0; // iterator
    int tokens = 1; // number of tokens
    int check = 0; // has it failed
    int count = 0; // number of valid passwords
    while(fgets(string,100,fp)) // read till eof
    {
        // read string in from the file
        //printf("%s", string); // print it
        for(i = 0; string[i] != '\0'; i++) // find the amount of tokens in the string
        {
            if(string[i] == ' ')
            {

                tokens++;
            }
        }
        string[i-1] = '\0'; // remove the \n
        //printf("done %d strings found\n", tokens);
        tokenPtr = strtok(string, " "); // tokenize the string
        arr = malloc(tokens * sizeof(char*)); // malloc array for number of strings
        for(i = 0; i < tokens; i++) // malloc a array for each string
        {                           // arr is an array of pointers to strings
            // for pt2 qsort(tokenPtr, strlen(tokenPtr), 1, (cmp));
            arr[i] = malloc(20 * sizeof(char));
            strcpy(arr[i], tokenPtr); // copy string into the newly allocated array
            tokenPtr = strtok(NULL, " ");
        }

        check = 0; // reset the check
        for(int j = 0; j < tokens; j++)
        {
            for(i = 0; i < tokens; i++)
            {
                if(strcmp(arr[j], arr[i]) == 0 && i != j)
                {
                    //printf("strings are the same\n");
                    check = 1; // check failed
                }
            }
        }
        if(check != 1) // if no strings were the same count passed increment it
        {
            count++;
        }
        for(i = 0; i < tokens; i++) // free the strings
        {
            free(arr[i]);
        }
        tokens = 1; // reset the ammount of strings

    }
    printf("valid passwords: %d\n", count);
    end = clock();
    double time_taken = ((double) (end - start)) / CLOCKS_PER_SEC;
    printf("program took %f seconds to execute\n", time_taken);
    return 0;

}