1 files changed, 78 insertions, 0 deletions
diff --git a/wk2/pset/caesar/caesar.c b/wk2/pset/caesar/caesar.c
new file mode 100644
index 0000000..70b4544
--- /dev/null
+++ b/wk2/pset/caesar/caesar.c
@@ -0,0 +1,78 @@
+#include <cs50.h>
+#include <ctype.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+
+bool only_digits(string phrase);
+int rotate(char c, int i);
+
+
+int main(int argc, string argv[])
+{
+    if (argc != 2 || only_digits(argv[1]) == false) {
+        printf("Usage: ./caesar key\n");
+        return 1;
+    } else {
+        int key = (atoi(argv[1])) % 26;
+        string plain = get_string("plaintext: ");
+        int plainlen = strlen(plain);
+        int cypher[plainlen];
+        printf("ciphertext: ");
+        for (int i = 0; i < plainlen; i++) {
+            cypher[i] = rotate(plain[i], key);
+            printf("%c", cypher[i]);
+        }
+        printf("\n");
+    }
+}
+
+
+bool only_digits(string phrase) {
+    for (int i = 0; phrase[i] != '\0'; i++) {
+        if (47 > phrase[i] || phrase[i] > 58) {
+            return false;
+        }
+    }
+    return true;
+}
+
+
+int rotate(char c, int i) {
+    if ((64 < c && c < 91) || (96 < c && c < 123)) {
+        c += i;
+        if (64 >= c || (c >= 91 && 96 >= c) || c >= 123) {
+            c -= 26;
+        }
+    }
+    return c;
+}
+
+
+
+/*
+Your program must accept a single command-line argument, a non-negative integer. Let’s call it *k*
+    for the sake of discussion.
+If your program is executed without any command-line arguments or with more than one command-line
+    argument, your program should print an error message of your choice (with printf) and return from
+    main a value of 1 (which tends to signify an error) immediately.
+If any of the characters of the command-line argument is not a decimal digit, your program should print
+    the message Usage: ./caesar key and return from main a value of 1.
+Do not assume that k will be less than or equal to 26. Your program should work for all non-negative
+    integral values of k less than 2^31-26. In other words, you don’t need to worry if your program eventually
+    breaks if the user chooses a value for k that’s too big or almost too big to fit in an int. (Recall
+    that an int can overflow.) But, even if k is greater than 26, alphabetical characters in your program’s
+    input should remain alphabetical characters in your program’s output. For instance, if k is 27, A should
+    not become \ even though \ is positions away from A in ASCII, per asciitable.com; A should become B,
+    since B is 27 positions away from A, provided you wrap around from Z to A.
+Your program must output plaintext: (with two spaces but without a newline) and then prompt the user for
+    a string of plaintext (using get_string).
+Your program must output ciphertext: (with one space but without a newline) followed by the plaintext’s
+    corresponding ciphertext, with each alphabetical character in the plaintext “rotated” by k positions;
+    non-alphabetical characters should be outputted unchanged.
+Your program must preserve case: capitalized letters, though rotated, must remain capitalized letters;
+    lowercase letters, though rotated, must remain lowercase letters.
+After outputting ciphertext, you should print a newline. Your program should then exit by returning 0
+    from main.
+*/