sicp练习1.18 基于加法、加倍和折半运算求两个整数之乘积

;double的功能是2*n(define (double n)  (+ n n))(double 5);havle-iter函数的功能是通过迭代获得n的一半的值,guess是初始猜测值(define (havle-iter guess n)  (cond ((not (integer? n)) (display "error: 原因havle函数的参数是整数\n"))        (( and (< (double guess) n) (<= (double (+ guess 1)) n)) (havle-iter (+ 1 guess) n))        (( and (> (double guess) n)) (havle-iter (- guess 1) n))        (( and (< (double guess) n) (> (double (+ guess 1)) n)) (+ guess 0.5))        ((= (double guess) n) guess)));havle函数的功能是通过迭代获得n的一半的值,guess是初始猜测值是1(define (halve n)  (havle-iter 1 n))(halve 16)(halve 37)(halve 35.5);even?函数功能是判断n是否是偶数,如果是偶数值为#t,否则为#f(define (even? n)  (cond ((= n 0) #t)        ((= n 1) #f)        ((and (integer? n) (< n 0)) (even? (+ n 2)))        ((and (integer? n) (> n 1)) (even? (- n 2)))        (else #f)))(even? 13)(even? 22)(even? 22.5);*函数的功能是a乘以b(define (* a b)  (cond ((or (= a 0) (= b 0)) 0)        ((= a 1) b)        ((even? a) (* (halve a) (double b)))        (else (+ (* (- a 1) (- b 1)) a b -1))))(* 3 4)