Vigenere Cipher in C

This is a C Program to implement Vigenere Cipher. Implement a Vigenère cypher, both encryption and decryption. The program should handle keys and text of unequal length, and should capitalize everything and discard non-alphabetic characters. If your program handles non-alphabetic characters in another way, make a note of it.

Here is source code of the C Program to Implement the Vigenere Cypher. The C program is successfully compiled and run on a Linux system. The program output is also shown below.

```
#include <stdio.h>
```
```
#include <stdlib.h>
```
```
#include <string.h>
```
```
#include <ctype.h>
```
```
 
```
```
void upper_case(char *src) {
```
```
    while (*src != '\0') {
```
```
        if (islower(*src))
```
```
            *src &= ~0x20;
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        src++;
```
```
    }
```
```
}
```
```
 
```

char* encipher(const char *src, char *key, int is_encode) {

```
    int i, klen, slen;
```
```
    char *dest;
```
```
 
```
```
    dest = strdup(src);
```
```
    upper_case(dest);
```
```
    upper_case(key);
```
```
 
```
```
    /* strip out non-letters */
```

    for (i = 0, slen = 0; dest[slen] != '\0'; slen++)

```
        if (isupper(dest[slen]))
```
```
            dest[i++] = dest[slen];
```
```
 
```

    dest[slen = i] = '\0'; /* null pad it, make it safe to use */

```
 
```
```
    klen = strlen(key);
```
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    for (i = 0; i < slen; i++) {
```
```
        if (!isupper(dest[i]))
```
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            continue;
```

        dest[i] = 'A' + (is_encode ? dest[i] - 'A' + key[i % klen] - 'A'

                : dest[i] - key[i % klen] + 26) % 26;

```
    }
```
```
 
```
```
    return dest;
```
```
}
```
```
 
```
```
int main() {
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    const char *str = "Beware the Jabberwock, my son! The jaws that bite, "

```
        "the claws that catch!";
```
```
    const char *cod, *dec;
```
```
    char key[] = "VIGENERECIPHER";
```
```
 
```
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    printf("Text: %s\n", str);
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    printf("key:  %s\n", key);
```
```
 
```
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    cod = encipher(str, key, 1);
```
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    printf("Code: %s\n", cod);
```
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    dec = encipher(cod, key, 0);
```
```
    printf("Back: %s\n", dec);
```
```
 
```

    /* free(dec); free(cod); *//* nah */

```
    return 0;
```
```
}
```

Output:

$ gcc VigenereCipher.c
$ ./a.out
 
Text: Beware the Jabberwock, my son! The jaws that bite, the claws that catch!
key:  VIGENERECIPHER
Code: WMCEEIKLGRPIFVMEUGXQPWQVIOIAVEYXUEKFKBTALVXTGAFXYEVKPAGY
Back: BEWARETHEJABBERWOCKMYSONTHEJAWSTHATBITETHECLAWSTHATCATCH

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