cs50 badcode

#include <cs50.h>
#include <stdio.h>
#include <ctype.h>
#include <string.h>
#include <stdlib.h>

int main(int argc, string argv[])
{
    string arr[] = {"A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q","R","S","T","U","V","W","X","Y","Z"};
    int key = atoi(argv[1]);
    string plaintext = get_string("plaintext: ");
    char cpystr[64];
    for (int i = 0; i < sizeof(plaintext); i++)
    {
        strncpy(cpystr, plaintext, 64);
    }
    int h = 0;
    for (h = 0; cpystr[h]!='\0'; h++)
    {
      if(cpystr[h] >= 'a' && cpystr[h] <= 'z')
      {
         cpystr[h] = cpystr[h] - 32;
      }
    }
    char cipher[64];
    printf("ciphertext: ");
    for (int i = 0; i < strlen(cpystr); i++)
    {
        cipher[i] = strcmp(&cpystr[i], arr[0]) + key;
        int val = cipher[i];
        printf("%s", arr[val]);
    }
    printf("\n");
}