Weird characters randomly appearing when converting int arr to string in C (with valid ASCII)

Question

This is a simple Caesar cipher implementation in C.

I take a pin, make a key from it, take a message, shift the ASCII value w.r.t the key, and output the hex value of each character in hex.

Upon using (as it appeared to me) any key , for the some (not all) messages results in the printing of an extra character upon decoding.

Example Cases :

Weird Char appearing :

Message : "hexa !"

Pin : 454545 & Key : 23

Ciphertext : (in hexa) " 51 4e 61 4a 9 a fffffff3 4e -6f " (-6f is simply used to terminate input)

Text given when decoding :

hexa !
e

Other keys generate other weird chars , like ' + ', for example. The weird char always appears on the next line.

The entire code is ~ 100 lines, so I wont paste it here, but it's available on GitHub . Don't use the windows .exe in this repo, it is of the older version, I'm trying to fix this issue before releasing this version.

The code where the issue is likely appearing is the encrypt() and decrypt() functions :

void encrypt() {
     char msg[3001], ch;
     int i,key, en[3001], count = 0;

     printf("\n");
     key = pin();
     getchar();
     printf("\nType Message - \n\n");
     fgets(msg,sizeof(msg),stdin);

     for (i=0; msg[i] != '\0'; i++) {
         ch=msg[i];
         int d = (ch - key);
         en[i] = d;
         count++;
     }

     printf("\nEncrypted message -\n\n");

     for (i=0; i <= count; i++) 
         printf("%x ", en[i]);

     printf("-6f");
}

void decrypt() {
     char msg[3001], ch;
     int i,key, en[3001],d;

     printf("\n");
     key = pin();
     printf("\nEnter encrypted message -\n\n");
     getchar();

     for (i=0; i <= 3001; i++) {
         scanf("%x",&d);

         if (d == -111) {
            msg[i] = '\0';
            break;
         } else {
            ch = d + key;
            msg[i] = ch;
         }
     }

     printf("\nDecrypted message -\n\n");
     puts(msg);
}

Your second `for` loop should probably be `i < count`, not `i <= count`. My preference would be `while(msg[i])` for both of those loops. — Robert Harvey, Aug 06 '20 at 16:01
Don't declare multiple variables on a single line. One declaration per line, always. — Robert Harvey, Aug 06 '20 at 16:02
No. It can cause problems. One declaration per line, please. — Robert Harvey, Aug 06 '20 at 16:03
@RobertHarvey your initial comment of i < count fixes my problem... — A P Jo, Aug 06 '20 at 16:04
@RobertHarvey I'm genuinely curious , what problems can/will it cause ? — A P Jo, Aug 06 '20 at 16:04
@RobertHarvey maybe publish you comment as answer so that I can accept it ? — A P Jo, Aug 06 '20 at 16:05
Note `fgets(msg,sizeof(msg),stdin);` saves the `'\n'` in `msg[]`. — chux - Reinstate Monica, Aug 06 '20 at 16:05
@chux-ReinstateMonica Yeah I've been quit bothered with that ... how do i remove it ? — A P Jo, Aug 06 '20 at 16:09
I've never heard about the argumentation to write all declarations belong to one type in one line in a relevant context. And it is indeed a stylistic choice. Doing like that could also decrease readability when it comes to too many variables. Grouping declaration per purpose is also a good concern. I agree that it helps in this specific case, but needs to think about new at each specific case. In short: I disagree with the "always" part. — RobertS supports Monica Cellio, Aug 06 '20 at 17:48
@RobertSsupportsMonicaCellio Style choices are best solved by following your group's coding standard. Preferable that standard can automatically check code. Else with competing choices, I favor the one easiest to maintain. If still tied, flip a coin. — chux - Reinstate Monica, Aug 06 '20 at 22:41

Robert Harvey · Accepted Answer · 2020-08-06T16:21:07.877

4

In your second for loop:

for(i = 0; i <= count; i++)

You are running off the end of the array (array indices start at zero, not one).

Change it to:

for(i = 0; i < count; i++)

Always put your variable declarations each on their own line.

int a, b, c = 0;        // only one variable is initialized.
char *src = 0, c = 0;   // c is of type char, not char*

fgets includes the trailing newline. If you don't want it, you have to strip it off.

int len = strlen(msg);
if(len > 0 && msg[len - 1] == '\n')
   msg[len - 1] = '\0';

edited Aug 06 '20 at 16:21

answered Aug 06 '20 at 16:12

Robert Harvey

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Regarding the last point another elegant way is using `strcspn()` as shown [here](https://stackoverflow.com/a/28462221/12139179). – RobertS supports Monica Cellio Aug 06 '20 at 17:41

Weird characters randomly appearing when converting int arr to string in C (with valid ASCII)

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