#include <stdio.h>
#include <cs50.h>
#include <string.h>
#define ALPHA_NUM 26

int main(int argc, char *argv[]) {

    // check argument number and argument key to be greater than -1
    if (argc != 2 || atoi(argv[1]) < 0) {
        printf("Usage (k >= 0):\n./caesar k \n");
        return 1;
    }

    int key = atoi(argv[1]) % ALPHA_NUM;

    // get plaintext from user
    printf("plaintext: ");
    string plaintext = get_string();
    printf("\n");

    string ciphertext = "";

    // encode plaintext
    size_t text_len = strlen(plaintext);
    for (int i = 0; i < text_len; ++i) {
        
    }



    return 0;
}

#include <stdio.h>
#include <cs50.h>

int main(int argc, char *argv[]) {

    // check entered key
    if (argc != 2 || atoi(argv[1]) < 0) {
        printf("Usage: ./caesar k\nWhere k is a non negative integer.\n");
        return 1;
    }

    int key = atoi(argv[1]);



    return 0;
}

--- 
+++ 
@@ -1,15 +1,30 @@
 #include <stdio.h>
 #include <cs50.h>
+#include <string.h>
+#define ALPHA_NUM 26
 
 int main(int argc, char *argv[]) {
 
-    // check entered key
+    // check argument number and argument key to be greater than -1
     if (argc != 2 || atoi(argv[1]) < 0) {
-        printf("Usage: ./caesar k\nWhere k is a non negative integer.\n");
+        printf("Usage (k >= 0):\n./caesar k \n");
         return 1;
     }
 
-    int key = atoi(argv[1]);
+    int key = atoi(argv[1]) % ALPHA_NUM;
+
+    // get plaintext from user
+    printf("plaintext: ");
+    string plaintext = get_string();
+    printf("\n");
+
+    string ciphertext = "";
+
+    // encode plaintext
+    size_t text_len = strlen(plaintext);
+    for (int i = 0; i < text_len; ++i) {
+        
+    }
 
 
 
Add  unfinished loop to encode message
