vigenere

#include<stdio.h>
#include<cs50.h>
#include<string.h>
#include<ctype.h>
 int main (int argc , string argv[])
 {
    string k = argv[1];
    //validating code
    if( argc!=2 )
    {
        printf("1\n");
        return 1;
    }
     for(int z=0;z<strlen(k);z++)
     {
        if(!isalpha(k[z]))
        {
            printf("1\n");
            return 1;

        }
     }
     //enciphering...
     string p = GetString();
     for(int i=0,j=0,x=strlen(p);i<x;i++)
     {

        if(isalpha(p[i]))
        {
            int j=i%strlen(k);

                if(isupper(p[i])&&isupper(k[j]))
                {
                    p[i]=(((p[i]-'A')+(k[j]-'A'))%26)+'A';
                    j++;
                }
                else
                if(islower(p[i])&&islower(k[j]))
                {
                    p[i]=(((p[i]-'a')+(k[j]-'a'))%26)+'a';
                    j++;
                }
                else
                if(isupper(p[i])&&islower(k[j]))
                {
                     p[i]=(((p[i]-'A')+(k[j]-'a'))%26)+'A';
                     j++;
                }
                else
                if(islower(p[i])&&isupper(k[j]))
                {
                    p[i]=(((p[i]-'a')+(k[j]-'A'))%26)+'a';
                    j++;
                }
        }
     }
        printf("%s\n",p);

        return 0;
 }