霍纳（Horner）规则是采用最少的乘法运算策略，求多项式 A(x) = a[n]x^n + a[n-1]x^(n-1) + ... + a[1]x^1 + a[0]x^0 在x处的值。
该规则为 A(x) = (...((a[n]x + a[n-1])x + ... + a[1])x + a[0])。利用霍纳规则，编写C语言程序对多项式进行求值。
解：
分别用迭代和递归两种方法来实现，解题代码分别如下：
<1> 迭代：
#include <stdio.h>int horner(int *array, int n, int x){ int result = array[n]; while(n) { result = result * x + array[--n]; } return result;}int main(void){ int result = 0, i = 0, x = 0, amount = 0; do { printf("Input the amount of coefficients(include zero.):"); scanf("%d", &amount); } while (amount <= 0); int a[amount]; printf("Input the cofficients:"); for (i = 0; i < amount; ++i) { scanf("%d", &a[i]); } printf("Input the x:"); scanf("%d", &x); result = horner(a, amount - 1, x); printf("The result is :%d", result); return 0;}<2> 递归：
#include <stdio.h>int horner(int *array, int n, int x){ if ( !n ) { return *array; } return horner(array + 1, n - 1, x) * x + *array;}int main(void){ int result = 0, i = 0, x = 0, amount = 0; do { printf("Input the amount of coefficients(include zero.):"); scanf("%d", &amount); } while (amount <= 0); int a[amount]; printf("Input the cofficients(Like:x,y,z or x y z):"); for (i = 0; i < amount; ++i) { scanf("%d", &a[i]); } printf("Input the x:"); scanf("%d", &x); result = horner(a, amount - 1, x); printf("The result is :%d", result); return 0;}