c++题目 不知道怎么弄 1. 编程序 用迭代法求a的立方根,求立方根的迭代公式为 ::Xi+1=（2*Xi）/3+a/

#include
#include
void main(void)
{
double a, fX, fXplus, fDiff, fRes;
printf("Enter a number: ");
scanf("%lf", &a);
fX = a;
fRes = pow(a, 1.0/3);
do
{
fXplus = fX * 2/3 + a / (3 * fX * fX);
fDiff = fXplus - fX;
fX = fXplus;
}
while((fDiff = 0.00001));
printf("nThe cube root of %lf is %lf.n", a, fX);
printf("The result of function is %lf.n", fRes);
}