Caesar Cipher Don't Allow Inputs

Question

I am trying to write a code on C that can do Caesar Encryption, but the code is not working and I couldn't find any mistakes. It's working neither in terminal nor in repl.it, even if I copy-paste a shared, trusted code and edit a bit to cover my expectations. The program doesn't allow the user to write inputs, except "key" part. It only shows all of the printf functions and that's it.

Here is my code:

#include <stdio.h>
int main() {

    int key, i;
    char text[30], c;

    printf("Please enter a number for key:\n");
    scanf("%d", &key);

    printf("Please enter a text for Caesar-Cipher:\n");
    scanf("%[^\n]s", text);

    for (i = 0; text[i] < '\0'; i++) {
        
        c = text[i];

        if (c>=65 && c<90) {
            c = c + key;
            
            if (c==90) {
                if (key!=0){
                    c = 64 + key;
                }
            }

        text[i] = c;   
        }

        else if (c>=97 && c<122) {
            c = c + key;

            if (c==122) {
                if (key!=0) {
                    c = 96 + key;
                }
            }

        text[i] = c;
        }
    }
    
    printf("The encrypted text is: %s\n", text);

    return 0;
}

`scanf("%[^\n]s", text);` the `s` does not belong there. `scanf("%[^\n]", text);` it should be. All teaching materials that use `%[^\n]s` are categorically wrong and should not be trusted for any use. — Antti Haapala -- Слава Україні, Jan 08 '21 at 00:45
In this case the easiest fix is to use `scanf(" %[^\n]", text)`, note the space. — Antti Haapala -- Слава Україні, Jan 08 '21 at 00:48
Okay, thanks. The space worked but why `s` does not belong there? I couldn't get it. And I tried it and it worked with `s` — Efe, Jan 08 '21 at 00:57
so how about you add all the rest of the letters like abcdefghijklmnopqrtuvwxyz twice there while at it. I just said that sources that suggest you should write `%[xxx]s` with `s` after the `]` are categorically wrong. — Antti Haapala -- Слава Україні, Jan 08 '21 at 02:16
That it doesn't harm in *this* case doesn't mean that it would work in some other case for example `scanf("%[^\n]s %[^\n]s", line1, line2);` — Antti Haapala -- Слава Україні, Jan 08 '21 at 02:19

alex01011 · Answer 1 · 2021-01-08T03:35:34.470

0

You are not consuming the newline character, try this:

scanf(" %29s", text);

or if you want space seperated words:

scanf(" %29[^\n]", text);

Also look at this question , scanf() leaves the new line char in the buffer

edited Jan 08 '21 at 03:35

answered Jan 08 '21 at 00:43

alex01011

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and caesar cipher is often used for sentences, for which the code would fail to work. – Antti Haapala -- Слава Україні Jan 08 '21 at 00:47
text is an array of 30 chars – alex01011 Jan 08 '21 at 00:48
@alex01011 `%s` matches a **single space-delimited word**. – Antti Haapala -- Слава Україні Jan 08 '21 at 00:49
i fail to see your point @AnttiHaapala – alex01011 Jan 08 '21 at 00:49
A sentence is a string of word**s**. – Antti Haapala -- Слава Україні Jan 08 '21 at 00:50
Well sure but I just adjusted that to the code he wrote to prevent overflow @AnttiHaapala – alex01011 Jan 08 '21 at 00:51
@alex01011 yes, I know. But the array should not be more than 30 chars. So it's on purpose. – Efe Jan 08 '21 at 01:00
yes but your code reads the **first word** of the sentence, unlike OP's code, so this is not much of an improvement. OPs code would have at least worked with `13 foo bar` on a single line. – Antti Haapala -- Слава Україні Jan 08 '21 at 02:20
@AnttiHaapala I have added that case too, thanks – alex01011 Jan 08 '21 at 03:35

Caesar Cipher Don't Allow Inputs

1 Answers1