caesar.c - shared from CS50 IDE

caesar.c

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

int c;
int k;
int p1;

int main(int argc, string argv[]) {
    if (argc == 0 || argc >2) {
        printf ("ERROR\n");
       return 1;
    }
     k = atoi(argv[1]);
     
     string p = GetString();
     printf("plaintext: %s\n", p);
     printf ("ciphertext: ");
     
     
     for (int i = 0, n = strlen(p); i < n; i++) {
            
            if (isalpha (p[i])) {
                
                if (isupper (p[i])) {
                    
                    p1 = p[i] - 65;
                    c = (p1 + k)%26 + 65;
                    printf ("%c", (char) c);
                }
                
                else if (islower (p[i])) {
                    p1 = p [i] - 97;
                    c = (p1 + k)%26 + 97;
                    printf ("%c", (char) c);
                }
                
            }
            if (isdigit (p[i])) {
                c = p[i];
                printf ("%c", (char) c);
            }
            if (ispunct (p[i])) {
                c = p[i];
                printf ("%c", (char) c);
            }
            
            if (isblank (p[i])) {
                c = p[i];
                printf ("%c", (char) c);
            }
        
     }
printf ("\n");
return 0;
}