Mono alphabetic cipher doesnt work correctly

Question

Here is my code. Substitution Cipher in C. But i got an error this line: char *encryption (char cipher_text[]) { function definition is not allowed here. I think probably "main" function place not right. How can i fix it? And by the way how can i generate random alphabet for this code? Thank you so much.

#include <stdio.h>
#include <stdlib.h>
#include <strings.h>
#include <ctype.h>
#include <string.h>


char *encryption (char cipher_text[]) {
            int i, val, j;
            printf("\n abcdefghijklmnopqrstuvwxyz \n");

if you want to generate a random alphabet, look into using the `rand()` function - you would want to generate a random number and mod it by 26, then add 97 to it, and store the variable in a `char`. See http://www.asciitable.com/index/asciifull.gif for why we add 97 — schil227, Nov 23 '16 at 14:45
`srand((unsigned int) time(NULL) ); char key = rand( ) % 26 + 'a';` i added this lines for random generate alphabet but i got an error : `cipher_text[i]=key[j];` subscripted value is not an array, pointer or vector. How can i fix it? — misshyde, Nov 23 '16 at 15:57

score 0 · Answer 1 · edited Nov 23 '16 at 15:02

0

You cannot define a function inside another one. encryption is defined in main :/

edited Nov 23 '16 at 15:02

µtex

900
5
12

answered Nov 23 '16 at 14:37

Eliot B.

162
11

score 0 · Answer 2 · edited May 23 '17 at 11:59

0

In C, you cannot declare a function inside another function, like you did. Here is your code that will compile:

#include <stdio.h>
#include <stdlib.h>
#include <strings.h>
#include <ctype.h>
#include <string.h>

char *encryption (char []);
void *decryption (char []);
char alpha [26]={'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z'};
char key[26];


char *encryption (char cipher_text[]) {
int i, val, j;
printf("enter the unique KEY of 26 character:");
scanf("%s", key);
printf("\n abcdefghijklmnopqrstuvwxyz \n");
printf ("%s", key);

for (i=0; i <strlen(cipher_text); i++) 
{
    for (j=0; j<26; j++)
    {
        if (alpha[j]== cipher_text[i]) {
            cipher_text[i]=key[j];
            break;
        }
    }
}

printf ("your message enc: %s", cipher_text);
return cipher_text; 
}

int main ()
{
    int i, key, choice, flag=0;
    char *c_text, msg[255];
    printf("\n Enter plain text:");
    scanf ("%[^\n]", msg);
    encryption(msg);
    return 0;
}

How to generate random characters is answered here.

edited May 23 '17 at 11:59

Community

1
1

answered Nov 23 '16 at 14:39

Honza Dejdar

947
7
19

thanks but i still got errors (using Xcode in OS X ) `char *cipher_text, msg[255];` (not c_text btw) this line says: unused variable ciphertext. program is working but just i entered the plaintext then program exit. :/ it didn't encrypt. Thank you so much. – misshyde Nov 23 '16 at 15:03
Well, you have to call the function from main. I've just added it to the code i posted. – Honza Dejdar Nov 23 '16 at 15:07
Are you sure you copied the code exactly? With the line almost at the end with the function call (`encryption(msg);`)? It works for me. – Honza Dejdar Nov 23 '16 at 15:15
ok, now working but i got errors about values :/ thank you so much. i will checked this encryption is true or false. – misshyde Nov 23 '16 at 15:22
No problem. You can accept this answer, if it answered your question. – Honza Dejdar Nov 23 '16 at 15:23
ok, thank you so much Honza. and can i ask a question for decryption after i write codes? how can i contact with you? :) – misshyde Nov 23 '16 at 15:30
I don't think there are private messages here on SO, so I suggest you ask in a new question. – Honza Dejdar Nov 23 '16 at 15:33
One last question: `srand((unsigned int) time(NULL) ); char key = rand( ) % 26 + 'a';` i added this lines for random generate alphabet but i got an error : `cipher_text[i]=key[j];` subscripted value is not an array, pointer or vector. How can i fix it? – misshyde Nov 23 '16 at 15:55
You are trying to acces single `char` `key` as an array using `[]` operator. Try it like this: `cipher_text[i]=key;` – Honza Dejdar Nov 23 '16 at 15:58
i added new answer you see the my whole code, then i will delete. – misshyde Nov 23 '16 at 16:03

Mono alphabetic cipher doesnt work correctly

2 Answers2