help with Caesar problem from Pset2

Question

EDIT:

Here is the new "only_digits" function that I'm struggling with:

bool only_digits(string s)
{
    for (int i = 0, j = strlen(s); i < j; i++)
    {
        if isdigit(s[i])
        {
            return 0;
        }
        else
        {
            printf("Usage: ./caesar key\n");
            return 1;
        }
    }
}

I think I understand from the comment below that I'm not including the return = 0 in the right place, so it's returning to the main function potentially before it's finished checking all the characters, is that right? I can't seem to figure out what I need to put there (before the return = 0) in order to tell it to continue checking until the end of the array.

Looking for some help figuring out the error I'm getting for line 44:

It seems like I can't transfer the value of a single location within "plaintext[]" to the same location in "ciphertext[]"? I created the string "ciphertext" with the idea that that is where the information will be stored from each function rotating the characters (or not, as necessary) and then eventually to be printed out at the end. Any help TIA!

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

bool only_digits(string s);
char rotate(char c, int n);

int main(int argc, string argv[])
{
    // make sure program is run with just one command line argument
    if (argc != 2)
    {
        printf("Usage: ./caesar key\n");
        return 1;
    }

    // make sure every digit in argv[1] is a digit
    only_digits(argv[1]);

    // convert argv[1] from a 'string' to an 'int' and store that number in variable "key"
    int key = atoi("argv[1]");

    // prompt user for plaintext
    string plaintext = get_string("plaintext:  ");

    // length of the plaintext
    int text_length = strlen(plaintext);

    // create string for ciphertext with the same length as the plaintext
    string ciphertext[text_length];

    // for each character in the plaintext
    for (int i = 0, j = text_length; i < j; i++)
    {
        // rotate the character only if it's a letter
        if (isalpha(plaintext[i]))
        {
            rotate(plaintext[i], key);
        }
        else
        {
            ciphertext[i] = plaintext[i];
        }
    }

    // print out the ciphertext
    printf("ciphertext: %s\n", ciphertext[text_length]);

}

bool only_digits(string s)
{
    for (i = 0, j = strlen(s); i < j; i++)
    {
        if (isdigit((char)s[i]) == 0)
        {
            printf("Usage: ./caesar key\n");
            return 1;
        }
    }
}

char rotate(char c, int n)
{
    char rotated_char;
    if (isupper(plaintext[i]))
    {
        // rotate n number of places forward in the alphabet, uppercase
        (((plaintext[i]) - 65) + key) % 26 = rotated_char;
        // return the result
        ciphertext[i] = rotated_char + plaintext[i];
    }
    else if (islower(plaintext[i]))
    {
        (((plaintext[i]) - 97) + key) % 26 = rotated_char;
        ciphertext[i] = rotated_char + plaintext[i];
    }
}

Answer 1

This declaration string ciphertext[text_length]; creates an array of strings. From the context it should be a char array, not a string array. Changing that will likely lead to cascading compile errors. And remember it needs to be null-terminated to make it a "real" string.

Warning: this int key = atoi("argv[1]") will set key to the string literal "argv[1]", not the contents of argv[1].

From EDIT: The error from only_digits function "non-void function does not return a value in all paths":

You know and I know that the program will take either the "if" path or the "else" path. However, the compiler does not know that. Function needs to return something if it has not returned in the for loop.