#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;
}

/*C guarantees that zero is never a valid address for data, 
so a return value of zero can be used to signal an abnormal 
event, in this case no space.*/

void afree(char *p){  /* free storage pointed to by p */
    if (p >= allocbuf && p < allocbuf + ALLOCSIZE)
		allocp = p;
}