CODEWITHSUNDEEP
c++
Iman Fakhari
Iman Fakhari

Reputation: 85

i faced with :Error 2 error C3861: 'fx': identifier not found

i'm not much familiar to define function in cpp, but as usual i defined mine like:

#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;
}

and i faced with 2 errors that say: Error 2 error C3861: 'fx': identifier not found Error 4 error C3861: 'dif': identifier not found so what should i do?

Upvotes: 0

Views: 526

Answers (2)

Avt
Avt

Reputation: 17043

Place function declarations

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

before using them.

using namespace std;

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

int main(){

Now your functions are unknown for compiler in place where you are trying to call them.

Upvotes: 1

Vlad from Moscow
Vlad from Moscow

Reputation: 311028

Any name shall be declared before its using. You are using function name fx but you placed its declaration (which at the same time its definition) after the usage of its name. Place before main its declaration

double fx (int power,int x);

The same is valid relative function dif

Upvotes: 0

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