c++ - 我面对 :Error 2 error C3861: 'fx' : identifier not found

Question

我不太熟悉在 cpp 中定义函数，但像往常一样，我这样定义我的函数:

#include<iostream>;
#include<Windows.h>;
using namespace std;
int main(){

int n;
int power;

//f(x) = x^power-n=0
cout << "please enter number of root: " << endl;
cin >> power;
cout << "what number you want to get root: "<< endl;
cin >> n;
double x = 2;//it's the first x0 that newton algorithm needs

for (int i = 0; i<20000 ;i++)
{
   //f(x) = x^power-n=0 , f'(x) = 2*x //fx:x^power
   x = x - (fx(power,x) - n)/dif(power,x);
}
cout << "answer is " << x << endl;
return 0;

}

double fx (int power,int x){
for (int i = 1; i<power; i++)
{
    x = x*x;    
}
return x;
}

double dif (int power,int x){
//f(x) = x^power-n=0 -> f'(x) = power * x^(power-1)
if(power>1)
{
     for(int i = 1; i<power-1 ;i++){
     x = x*x;
     }
x = x*power;
return x;
}
return 1;
}

我遇到了 2 个错误:错误 2 error C3861: 'fx': 找不到标识符错误 4 error C3861: 'dif': 找不到标识符那我该怎么办？

Answer 1

放置函数声明

double fx (int power,int x);
double dif (int power,int x);

在使用它们之前。

using namespace std;

double fx (int power,int x);
double dif (int power,int x);

int main(){

现在您的函数在您尝试调用它们的地方对于编译器来说是未知的。