CS50/substitution

substitution.c

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

int only_letters(string text);
int repeated(string text);
char rotate(char c, string key);

int main(int argc, string argv[])
{
    if (argc != 2)
    {
        printf("Usage: ./caesar key\n");
        return 1;
    }

    else if (strlen(argv[1]) < 26 || strlen(argv[1]) > 26)
    {
        printf("Key must contain 26 characters.\n");
        return 1;
    }

    else if (!only_letters(argv[1]))
    {
        printf("Key must contain only letters\n");
        return 1;
    }

    else if (!repeated(argv[1]))
    {
        printf("Letters must not be repeted\n");
        return 1;
    }
    else
    {
        string plaintext = get_string("plaintext: ");
        printf("ciphertext: ");

        for (int i = 0; i < strlen(plaintext); i++)
        {
            printf("%c", rotate(plaintext[i], argv[1]));
        }
        printf("\n");
    }
}

int only_letters(string text)
{
    for (int i = 0; text[i]!='\0'; ++i)
    {
        if(!isalpha(text[i]))
        {
            return 0;
        }

    }
    return 1;
}

int repeated(string text)
{
    int count = 0;

    for (int i = 0; i < strlen(text); ++i)
    {
        for (int j = 0; j < strlen(text); ++j)
        {
            if (toupper(text[i]) == toupper(text[j]))
            {
                count ++;
            }

        }
    }
    if (count != 26)
    {
        return 0;
    }
    else
    {
        return 1;
    }
}

char rotate(char c, string key)
{
    for (int i = 0; i <= 25; i++)
    {
        if(isalpha(c))
        {
            if (isupper(c))
            {
                char new = key[(c - 65)];
                return toupper(new);
            }

            else
            {
                char new = key[(c - 97)];
                return tolower(new);
            }
        }
        else
        {
            return c;
        }
    }
    return 0;
}