Wont Cipher Text

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

int main(int argc, string argv[])
{
    string s = GetString();
    int k = atoi(argv[1]);


    if(argc != 2)
    {
        return 1;  //ensures the propper amount of arguemnets
    }

    for(int i = 0; i == strlen(s); i++)
    {
        char c = s[i];
        if(isupper(c))//checks for uppercase
        {
            char caesar = (((c - 65) + k) % 26) + 65; //ciphers the text >> example (((65 - 65) + 1) MOD 26)+ 65 = 66 (B)
            printf("%c", caesar);
        }else
        if(islower(c))//checks for lowercase
        {
            char lowerCaesar = (((c - 97) + k) % 26) +65;//ciphers the text >> example (((97 - 97) + 1) MOD 26)+ 97 = 98 (b)
            printf("%c", lowerCaesar);
        }else
        {
            printf("%c", c); //prints non letters; ! , . - _ %
        }

    }
    printf("\n"); // prints the newline
}