vigenere.c

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

int shift(char c);

int main(int argc, string argv[])
{
    string key = argv[1];
    if (argc== 2)
     {

        for(int i=0; i<strlen(key); i++)
        {
           if(isalpha(key[i]))
           {
                continue;
           }
           else
           {
               printf("Usage: ./vigenere keyboard\n");
               return 1;
           }
        }

    }
    else
    {
        printf("Usage: ./vigenere keyboard\n");
        return 1;
    }

    string text=get_string("plaintext: ");
    printf("ciphertext: ");
    int ktracker=strlen(key);
    int counter=0;
    for(int i=0;i<strlen(text);i++)
    {
        if(text[i]== '\40')
        {
            printf("%c",text[i]);
        }
        else
        {
            printf("%c",(text[i]+shift(key[counter%ktracker])));
            counter++;
        }

    }
    printf("\n");
}

int shift(char c)
{
   int ans=0;
   if(isupper(c))
   {
      ans=((c-65) % 26);
   }

   else if(islower(c))
   {

      ans=((c-97) % 26);
   }
   return ans;
}