Question

试用74LS290构成九进制计数器

Answer 1

#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;
}

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