Palindrome thingy

// I...got a little carried away...

#include <stdio.h>

void modify_buffer(char *buffer){
    int i = 1;

    while(*buffer){
        *buffer += ++i * strlen(buffer);
        *buffer = ((*buffer - 'A') % 26) + 'A';
        buffer++;
    }
}

int main(){
    char buffer[10] = "ABCDEFG";
    char buffer2[10] = "ABCDEFGH";

    modify_buffer(buffer);
    modify_buffer(buffer2);

    printf("Buffer: %s\n", buffer); // OTWXWTO
    printf("Buffer2: %s\n", buffer2); // QWACCAWQ
}