Euler's Number Loop

[owCkSL3A]

I have to find euler's number to whatever the user's desired accuracy is (.001,.0001....) i cant figure out why my code is returning inf as the answer for everything. I have looked over my code many times and hand wrote a few loops but i cant find any issues. Im sure its something small but i could use some help. thanks.

the seris i am using is

1+ 1/1 + 1/1*2 + 1/ 1*2*3 and so on .....




Updated code

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



int fact(int n);

int main()
{
	double ans;
	double acc;
	double e = 0;
	double e2 = 1;
	double diff;
	int x = 0;
	
	cin >> acc;

	do
	{
		e = 1 + 1 / fact(x);

		diff = abs(e - e2);

		e2 = e;
		x++;

	} while (diff > acc);

	ans = e;

	cout << ans << endl;




	system("pause");
	return 0;
}

int fact(int n)
{
	int i;
	int factorial;

	for (i = 0; i <= n; i++)
	{
		if (i == 0)
			factorial = 1;
		else
			factorial *= i;
	}
	
	return factorial;
}

[TheIdeasMan]

Hi,

Your function returns 0.0 so on line 24, that is the value being used, hence the inf. Instead of modifying a, just return the factorial value.

double i;
	double n = a;
	double factorial;

	for (i = 0; i <= n; i++)

Doubles are not represented exactly, so one shouldn't use them in a for loop. And using them in equality comparisons won't always work either.

Why do you need a double for a factorial anyway? Just use std::size_t, and in main use static_cast<double>(a) to cast it to double.

Line 58 can be written factorial *= i;

Good Luck !!

[owCkSL3A]

I changed the factorial function to int values since the doubles could be causing some issues.

Now every accuracy is being displayed with an answer of 2 or 1

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



int fact(int n);

int main()
{
	double ans;
	double acc;
	double e = 0;
	double e2 = 1;
	double diff;
	int x = 0;
	
	cin >> acc;

	do
	{
		e = 1 + 1 / fact(x);

		diff = abs(e - e2);

		e2 = e;
		x++;

	} while (diff > acc);

	ans = e;

	cout << ans << endl;




	system("pause");
	return 0;
}

int fact(int n)
{
	int i;
	int factorial;

	for (i = 0; i <= n; i++)
	{
		if (i == 0)
			factorial = 1;
		else
			factorial *= i;
	}
	
	return factorial;
}

[TheIdeasMan]

Now every accuracy is being displayed with an answer of 2 or 1

TheIdeasMan wrote:

Just use std::size_t, and in main use static_cast<double>(a) to cast it to double.

You didn't cast the result, so now it does integer division :+)

Edit:

You can force the result to be double by always putting numbers before and after the decimal point:

e = 1.0 + 1.0 / fact(x);

This will do an implicit cast.

[owCkSL3A]

I tried that with the code above and it is still doing the same thing. Any suggestions?

[TheIdeasMan]

With factorial *= i; , i is initially zero, so factorial will always be zero. Sorry I didn't notice that earlier :+)

[owCkSL3A]

I have made both of thoes changes and am still getting errors.

Could it possibly be an issue within my formula for calculating e?

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



int fact(int n);

int main()
{
	double ans;
	double acc;
	double e = 0;
	double e2 = 1;
	double diff;
	int x = 1;

	cin >> acc;

	do
	{
		e = 1.0 + 1.0 / fact(x);

		diff = abs(e - e2);

		e2 = e;
		x++;

	} while (diff > acc);

	ans = e;

	cout << ans << endl;




	system("pause");
	return 0;
}

int fact(int n)
{
	int i;
	int factorial;

	for (i = 1; i <= n; i++)
	{
		if (i == 0)
			factorial = 1;
		else
			factorial *= i;
	}

	return factorial;
}

[TheIdeasMan]

Compilation, with warnings turned on:

In function 'int main()':
54:18: warning: 'factorial' may be used uninitialized in this function [-Wmaybe-uninitialized]
7:6: note: 'factorial' was declared here In function 'int fact(int)':
57:9: warning: 'factorial' may be used uninitialized in this function [-Wmaybe-uninitialized]

Always initialise variables to something.

[owCkSL3A]

To simplify things i decided to take the function to find the factorial and do the same thing in the formula itself.

this is my code

now i am just trying to get the math correct. i do belive that the factorial is correct and that i just need to correct a few small mistakes in the math. is there anything you see that i may need to correct?

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



double fact(double& a);

void main()
{
	double acc;
	double dif;
	double i=1;
	double x = 1;
	double e;
	double e2=1;

	cin >> acc;

	do
	{
		i *= x;
		x++;
		e = 1 + 1 / i;

		dif = abs(e - e2);
			
		cout << endl << e << endl;
	} while (dif > acc);

	
		
	cout << e;


	system("pause");
	return;
}

[TheIdeasMan]

Hi,

Using your previous code, some poor man's debugging:

do
	{
		e = 1.0 + 1.0 / fact(x);
                cout << "e = " << e << endl;
		diff = abs(e - e2);

		e2 = e;
		x++;

	} while (diff > acc);

Can you see what's happening there?