1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
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.
*/
|
