Minimal caesar cipher implementation for CS50

caesar.c

#include<stdio.h>
#include<stdlib.h>
#include<ctype.h>
#include<cs50.h>    // Can be commented out if using test word
//char c[] = "hello";   // Uncomment these lines to use test word "hello".
//char *p = &c[0];
int main(int argc, char * argv[]) {
 char k=(argc>1)?k=atoi(*++argv):0;
 if((argc<2)||(k<=0)){printf("Bad number.\n");return 1;}
 else{
  string p=GetString(); // Comment this line out if using test word.
  while(*p!=0) printf("%c",((isalpha(*p))?((((*p++-((isupper(*p))?65:97))+k)%26)+((isupper(*p))?65:97)):*p++));
  return 0;
}}