Viginere

#include <stdio.h>#include <cs50.h>#include <string.h>#include <stdlib.h>#include <ctype.h>
int main(int argc, string argv[])                   // take the cipher integer as a command line arg{   
    string k = argv[1];                             // pulling the string out of the argv array
    if(argc != 2)                                   // check if there are any command line arguments                                                    // if there are no command-line arguments or too many, return an error code 1    {        printf("ERROR: invalid command line argument\n");        return 1;    }
    for(int n=0; n<strlen(k); n++)    {        if(isalpha(k[n]) == 0)        {            printf("ERROR: invalid command line argument\n");            return 1;        }    }
    int l[strlen(k)];
    for(int h = 0; h<strlen(k); h++)                // going through the key array    {        k[h] = toupper(k[h]);                       // standardizing the key        k[h] = k[h];                                // pulling the ascii out to make the key cooincide with 0-26 values        l[h] = (int) k[h] - 65;                     // I may need to convert the string in k[] to an int
        // printf("this is the integer value of my key: %i\n", l[h]);   // just checking    }
    printf("plaintext: ");                          // prompt for plaintext    string s = get_string();                        // get string
    int j = 0;
    printf("ciphertext: ");    for(int i = 0; i<strlen(s); i++)    {        // convert plaintext to ciphertext, ensure that numbers are unchanged, ensure that case is preserved        // I think we want to take the cipher key string (array), convert it to 0-26 values in an array, then iterate through both        // the string to be enciphered s[i], and the key array k[j] since the key array, may be shorter than the string to be enciphered,        // we will want to take the modulus of the key array length (strlen() )        // we also want to decouple k[j] from incrementing with i, because we don't advance the cipher key on non-alpha characters


        if(isupper(s[i]) != 0)                          // checking for upper case characters        {            s[i] = (((s[i] + l[j]) - 65) % 26) + 65;    // if the cipher is larger than 26, it needs to wrap around. I think the solution                                                        // is going to be algebraic, not arithmetic. the ASCII table doesn't start at 26, I need to modify the modulo to make this work.        }
        if(islower(s[i]) != 0)                          // check if lower case char. determining alpha by omission        {            s[i] = (((s[i] + l[j]) - 97) % 26) + 97;    // shift ascii values down to zero, encipher, shift ascii values back up        }
        if(isalpha(s[i]) != 0)                          // increment j only if the character in s[i] is alpha        {            j++;            j = j % strlen(k);        }

    // print ciphertext    printf("%c", s[i]); // Test OK    }
    // return char and return no error    printf("\n");    return 0;}