C code for NONRECURSIVE IMPLEMENTATION OF QUICKSORT

# define STACKSIZE 50

void quicksort(int x[], int n)

{

int i,j;

struct stack_info{

int l;

int u;

}bounds;

struct stack_tag{

int stacktop;

struct stack_info limits[STACKSIZE];

}STACK;

STACK.stacktop=-1;

bounds.l=0;

bounds.u=n - 1;

push(&STACK,&bounds);

while(!empty(&STACK))

{

pop(&STACK,&bounds);

while(bounds.u > bounds.l)

{

partition(x,bounds.l,bounds.u,&j);

if((j - bounds.l) > (bounds.u - j))

{

i=bounds.u;

bounds.u=j - 1;

push(&STACK,&bounds);

bounds.l=j + 1;

bounds.u=i;

}

else

{

i=bounds.l;

bounds.l=j + 1;

push(&STACK,&bounds);

bounds.l=i;

bounds.u=j - 1;

} /* end if */

} /* end while */

}/* end while */

return;

} /* end quicksort */

int emtpy (struct stack_tag * stackptr)

{

if( stackptr->stack.top == -1)

return (1);

else

return (0);

} /* end empty*

void pop (struct stack_tag * stackptr, struct stack_info * data)

{

if empty (stackptr)

{

printf (“%s\n”, “stack underflow”);

}

data=&(stackptr-> limits [stackptr->stacktop]);

-- (stackptr->stacktop);

return;

}

void push (struct stack_tag * stackptr, struct stack_info *data)

{

int p;

p=++(stackptr->stacktop);

stackptr->limits[p].l = data->l;

stackptr->limits [p].u = data->u;

return;

} /*end push.; note no checking for stack overflow */