l37.1a

<B>Digital的Unix操作系统VAX 4.2源码</B>

#print
Let's try a recursive function.  Write a subroutine
    power(x,n)
which computes x to the power n by the following
algorithm:
 1. if n is zero return 1.
 2. if n is odd return x*power(x,n-1).
 3. if n is even return the square of
    power(x,n/2).
You may assume than x and n are integers, n>=0.
If n is negative return 0 for an answer.
Put your routine on a file "power.c".  Compile
it and test it; then type "ready".
#once #create tzaqc.c
main()
{
if (power(-1,-1) != 0) 
		return(1);
	if (power(-3,2) != 9) 
		return(1);
	if (power(2,12) != 4096) 
		return(1);
	if (power(3,5) !=  243) 
		return(1);
	if (power(-5, 5) != -3125) 
		return(1);
	if (power(7,3) != 343) 
		return(1);
	if (power(7,4) != 2401) 
		return(1);
	if (power(3,7) != 2187) 
		return(1);
	if (power(2,10) != 1024) 
		return(1);
	return(0);
}
#user
cc tzaqc.c power.o
a.out
#succeed
/*  a possible solution */
power(x, n)
{
	int k;

	if (n < 0)
		return(0);
	if (n == 0)
		return(1);
	if (n%2 == 1)
		return(x * power(x, n-1));
	k = power(x, n/2);
	return(k*k);
}
#log
#next
40.1a 10