Infinite loop + factorial

[Tod85]

Hi Guys,

I have a task that I need a hand with as it seems I am not getting it the way I want it to work.

Basically the task is to do a C++ code that does "1 + Sum = 1 + ( 1/(2.1)! + 1/(2.2)! + 1/(2.3)! + ...) = 1 + ( ½ + 1/(1.2.3.4) + 1/(1.2.3.4.5.6) + ... )". Epsilon is 10^-6 and it needs to print out each result untill it reaches the epsilon //unfortunatly I am unable to paste the math formula here but I think that is what it needs to do.

So, I have been able to do the following // had help from a friend who knows C but not C++
C++, pasted just now:

1 int main() {
2 double sum = 1;
3 int k = 1;
4 double previous_sum = 1, this_sum;
5 double epsilon = 10^-6;
6
7 while (1) { // until k=infinity
8 this_sum = 1/(double)bang(2*k);
9 sum += this_sum;
10 if ( previous_sum - this_sum < epsilon ) {
11 break; // reached desired approximation
12 }
13 previous_sum = this_sum;
14 k++;
15 cout << "For k=" + k + ", the result is: " + sum;
16 }
17 cout << "Final result is: " + sum;
18 }
19
20 int bang( int to ) {
21 int result=1;
22 for ( int i=1; i <= to; i++ ) {
23 result *= i;
24 }
25 return result;
26 }

What I get is :
"In function 'int main()':
Line 8: error: 'bang' was not declared in this scope
compilation terminated due to -Wfatal-errors."

Can anyone help with my code or do share theirs that can achiove this sum

[Peter87]

You have to declare bang before it can be used. Place this above main:
int bang(int);


^ is the bitwise xor operator.
double epsilon = 10^-6;
should be written
double epsilon = 10e-6;

[Darkmaster]

fixed the errors and edited, so people can read it easily, but this is still not good programming style.

#include <iostream>


int bang(int to);

int bang(int to) 
{
	int result=1;
	for ( int i=1; i <= to; i++ ) 
	{
		result *= i;
	}
	return result;
}


int main() 
{
	double sum = 1;
	int k = 1;
	double previous_sum = 1, this_sum;
	double epsilon = 10e-6;

	while(1) // until k=infinity
	{
		this_sum = 1/(double)bang(2*k);
		sum += this_sum;
		if ( previous_sum - this_sum < epsilon ) 
		{
			break; // reached desired approximation
		}
		previous_sum = this_sum;
		k++;
		std::cout << "For k=" << k << ", the result is: " << sum;
	}
	std::cout << "Final result is: " << sum;
}

[Tod85]

Cheers Darkmaster!

Im in the office now and don't have a good compilator. I am using an online tool (http://codepad.org) which is giving me the below after I run the code in it:

"In function 'int main()':
Line 36: error: expected `}' at end of input
compilation terminated due to -Wfatal-errors."

I am sure that it is to do with the compilator, thogh. I am really below beginner so exuse my lack of knowledge and style. Also, you may find it to be lame but can you please let me know why yours start with #include <iostream> and ends with std::cout when I have been told it is to start with 1 int main().

Cheers,
Tod

[Tod85]

Gees, I was blind!

Thanks again Darkmaster! You are the MAAA!

[Darkmaster]

the includes are always on top since you first need to include libraries before you can use them in your code.
here i include iostream, which is needed for the output via cout;

the cout is at the end of the main, i didn't change that.

i placed the bang function above the main(), it's common to keep the main as last function, this way it is easy to find.