#define ALLOCSIZE 10000 /* size of available space */

static char allocbuf[ALLOCSIZE];  /* storage for alloc */
static char *allocp = allocbuf;   /* next free position */

char *alloc(int n)  /* return pointer to n characters */
{
    if (allocbuf + ALLOCSIZE - allocp >= n) { /* it fits */
        allocp += n;
        return allocp - n; /* old p */
    } else      /* not enough room */
        return 0;
}