mistake in the code

[rapids79]

I am trying to write a function that calculates the sine of a given angle. The code works fine if the angle in degrees is less than 100...once the angle becomes greater than 100..the result is a large value. I don't know what I am doing wrong. Can someone point out the mistake...thanks a ton.

/*Calculate sin x */
typedef unsigned char u8;
typedef double u32;

double pow(u32 , int );
int fact(int );

#define PI 3.1415926

#include<stdio.h>

int main()
{
	/*Angle being converted to radians*/
	u32 angle_in_radians = 45 * (PI/180);
	double sum =0;
	int n = 1,i=0;

	for(i=0; i<=16; i++)
	{
		/*calculate sin(x)*/
		sum += pow( -1, i ) * pow( angle_in_radians, n )/fact(n);
		n+=2;
	}
	printf("\nSIN is %f\n", sum);
	getchar();
	return 0;
}

double pow(u32 angle_in_radians, int n)
{
	int power = 0;
	if(n == 0)
		return 1;
	
	else return angle_in_radians * pow(angle_in_radians, n-1);

	return power;
}

int fact(int n)
{
	if(n == 0)
		return 1;

	else return n * fact(n-1);
}

[Adak]

Why aren't you including math.h?

Looks like an overflow problem, at first glance.

[rapids79]

Thanks for the reply..Overflow problem??? I don't exactly understand where exactly that is coming into picture here. could you please elaborate? thanks..

[sree_ec]

I am trying to write a function that calculates the sine of a given angle. The code works fine if the angle in degrees is less than 100...once the angle becomes greater than 100..the result is a large value. I don't know what I am doing wrong. Can someone point out the mistake...thanks a ton.

/*Calculate sin x */
typedef unsigned char u8;
typedef double u32;

double pow(u32 , int );
int fact(int );

#define PI 3.1415926

#include<stdio.h>

int main()
{
	/*Angle being converted to radians*/
	u32 angle_in_radians = 45 * (PI/180);
	double sum =0;
	int n = 1,i=0;

	for(i=0; i<=16; i++)
	{
		/*calculate sin(x)*/
		sum += pow( -1, i ) * pow( angle_in_radians, n )/fact(n);
		n+=2;
	}
	printf("\nSIN is %f\n", sum);
	getchar();
	return 0;
}

double pow(u32 angle_in_radians, int n)
{
	int power = 0;
	if(n == 0)
		return 1;
	
	else return angle_in_radians * pow(angle_in_radians, n-1);

	return power;
}

int fact(int n)
{
	if(n == 0)
		return 1;

	else return n * fact(n-1);
}

As Adak already said , it looks like an overflow.
Your factorial function returns an int value.
By the time you reach your i 8 or 9, n would have reached 17 or 19 and then its factorial is going to be a huge value which your signed int wont be able to handle. Which will surely cause your output to go wrong.
Try with modifying the factorial function such that it returns a higher precision value.

Some more things, you have defined pow() by yourself. It is already available in c in math library. so it could have been avoided.

Even in your pow() function the local variable seems to be of no use...

Please avoid using

#
typedef double u32;

typedef s like this.. it will confuse people... Usually u32 will strike as Unsigned data type with 32 bits [atleast for me].. more often used for 'unsigned int' in 32 bit systems.

[rapids79]

Thanks for the clarification..problem solved...Thanks again...I'm marking this thread as solved.

[rapids79]

Thanks for the clarification...problem solved...thanks again..will mark this thread as solved.