factorial function in a formula

[tlox]

(I am trying to write a c++ program which computes sine of an angle without using c math library.I came up with a formula for this problem.The formula should use a factorial function in the program.I have a problem in doing this and hence i posted my code here for you to help me. The code is as below.Thank you in advance.)

#include<iostream>
#include<cmath>
using namespace std;

double num();
void for_r();
void for_d();
int factorial();

int main()
{
	double x2, x;
	char choice;
	
	cout<<"Please enter an angle value \n";
	cin>>x;
	cout<<"Is the angle value in Degree or Radian?"<<endl;
	cout<<"Type D if its in degree "<<endl;
	cout<<"Type R if its in radian "<<endl;
	cin >> choice;
	
	switch(choice)
{
	case 'R':
	for_r();
	break;
	case 'r':
	for_r();
	break;
	case 'D':
	for_d();
	break;
	case 'd':
	for_d();
	break;
	default:
	cout<<"Wrong input"<<endl;
	}
	cout<<"sin(x) = "<<num<<endl;
	return 0;
   }  
void for_r(){
	 
	int n = 3; 
	double x2= 0, b, PI,r;
	
	double sum = num();
			
	for(int i = 1;sum > 0.000001; i++){
			if(i == 1){
			   x2 = num() - (pow(num(),n) /factorial() ); 
			   n = n + 2;
	   }
		  else 
		    {
			   x2 = (x2 + ((pow(num(),n))/(factorial())) - (pow(num(),n+2) / factorial()+2));
			   n = n + 4;
		   }
	} 
 }
void for_d(){
	
	double x2= 0, PI, r;
    int  n = 3; 
	
	 r =( num() * (PI /180));
	     
	   double sum = num();
		for(int i = 1;sum > 0.000001; i++){
			if(i == 1){
			   x2 = num() - ((pow(num(),n) /factorial()));
			   n = n + 2;
	   }
		  else 
		    {
			   x2 = (x2 + ((pow(num(),n))/factorial() ) - (pow(num(),n+2) /(factorial()+2)));
			   n = n + 4;
		   }
	 }
 }
double num(){
	
	int n = 3;
	double x2, x;
	
	x2 =(x2 + ((pow(num(),n))/factorial())-(pow(num(),n+2)/(factorial()+2)));
	n = n + 4;
		
	return (x2);
	}

int factorial(){
	
	int n = 3;
   return (n * factorial ()-1);
}

[Narue]

>I have a problem in doing this and hence i posted my code here for you to help me.
That's nice, but you forgot to tell us what the problem is. No offense intended, but I have more interesting things to work on. I'm more likely to work on my own code than troubleshoot your code for an unspecified "problem".

[tlox]

>I have a problem in doing this and hence i posted my code here for you to help me.
That's nice, but you forgot to tell us what the problem is. No offense intended, but I have more interesting things to work on. I'm more likely to work on my own code than troubleshoot your code for an unspecified "problem".

The problem is that i can not call the factorial function.Also i think the formula i used might be wrong.

[vmanes]

Factorial function is really pretty easy - often used in any tutorial about recursion, although a method using a loop is more efficient.

Keep in mind that factorial grows very fast - depending on how many iterations your calculation for sine goes, unsigned int may not be a suitable data type to return from your factorial function.

And review your material on writing functions - you need to be passing some arguments (parameters) to the ones you have in your program, but you're not.

Google is your friend.