Code:
#define MAX_SIZE ???

void write (const char *);
void write_LCD (const char *);

void write (const char * input)
{
    static char output[MAX_SIZE];
    char c;

    while (c = *input++, c)
    {
        if ('A' == c)
        {
             *output++ = ...
             *output++ = ...
             *output++ = ...
             ...
        }

        if ('B' == c)
           ...
    }

    *output = '\0';

    write_LCD (output);
}