I'm facing the CS50's substitution problem. It works, even though the code is not very optimized.

The problem is that i had to add this line of code at the end to make it work: `

cipher_text[strlen(plain_text)] = '\0';

`

otherwise the lenght of the cipher_text is longer than expected.

Can you tell me why?

this is the code i've written.

`

#include 
#include 
#include 
#include 

int main(int argc, string argv[])
{
    // check if there's 1 argument, if there are > 1 or < 0 print error message and return 1
    if (argc != 2)
    {
        printf("Error, type 1 command\n");
        return 1;
    }

    string key = argv[1];
    long lenght = strlen(key);

    // check if the key is valid (26 characters) or not, if not return 1 and print error
    if (lenght != 26)
    {
        printf("Key must contain 26 characters.\n");
        return 1;
    }

    // iterate throughout the key, element after element whith the 1st for loop
        //check if contains letters or something else in the 1st if
        //make the key all lower in order to compare letter repetition in the else if
        //check for double letters (compare every letter (key[i]) with all the other letters) in the second for loop
    for (int i = 0 ; i < lenght ; i++)
    {
        if (isalpha(key[i]) == 0) //(key[i] < 65 || key[i] > 90) && (key[i] < 97 || key[i] > 122))
        {
            printf("Key must contain only letters\n");
            return 1;
        }
        else if (isupper(key[i]))
        {
            key[i] = tolower(key[i]);
        }
        for (int j = 0 ; j < lenght ; j++)
        {
            if (j != i && key[j] == key[i])
            {
                printf("You can't repeat letters in key (you've repeated the letter %c)\n", key[j]);
                return 1;
            }
        }
    }

    //ask user for the text to cipher
    string plain_text = get_string("plaintext:  ");

    char alphabet[] = "abcdefghijklmnopqrstuvwxyz";
    char ALPHABET[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

    char cipher_text[strlen(plain_text)];

    // iterate through every index in plain_text
        //if it is not alphabetical, add it to cipher text
        //otherwise, check if it is lower or upper, and add to cipher_text
        //
    for (int j = 0; j < strlen(plain_text) ; j++)
    {
        if (isalpha(plain_text[j]) == 0)
        {
            cipher_text[j] = plain_text[j];
        }

        for (int x = 0 ; x < lenght ; x++)
        {
            if(islower(plain_text[j]))
            {
                if (plain_text[j] == alphabet[x])
                {
                cipher_text[j] = key[x];
                }
            }
            else if (isupper(plain_text[j]))
            {
                if (plain_text[j] == ALPHABET[x])
                {
                cipher_text[j] = toupper(key[x]);
                }
            }

        }


    }

    cipher_text[strlen(plain_text)] = '\0';

    printf("ciphertext: %s\n", cipher_text);

    return 0;

}

`