simple question

[juliam921]

I have to calculate the value of e which is equal to

e = 1 + 1/1! + 1/2! + 1/3! ...

i know that the factorial for a value is calculated by:

for( int i = 1; i <=n; i++)
fact = fact * i;

JOptionPane.showMessageDialog(null, &quot;fact = &quot; + fact);

so how do i modify this to calculate the value of e?

i tried the following, but my logic is wrong.

for( int i = 1; i <=n; i++)
fact = fact * i;

e = e + 1/fact ;
JOptionPane.showMessageDialog(null, &quot;e = &quot; + e);

As you can see, I am new to Java. Any help would be appreciated!
-Julia

 

[prosper]

class cal
      {
       public static void main(String args[])
              {
               int n = 3, fact=1;
               double e = 1.0;
               for (int i=1; i<=n; i++)
                   {
                    fact*=i;
                    System.out.println(fact);
                    e = e + 1/(double)fact; // an integer literal 1 is divided by a double literal fact will give a double result
                    //e = e + 1/fact; //will not give correct result
                    System.out.println(e);
                   }
              }
      }
// here is the rules
//[URL unfurl="true"]http://www.cafeaulait.org/course/week2/19.html[/URL]

 

[juliam921]

That logic does not work. I think maybe I need a nested loop. When I do the above, no matter what I put in for n, I get fact = 1, e = 2.0.

 

[jstreich]

float e = 0;
int n = 3;
for(int i = 1; i <= n; ++i)
{
  int fact = 1;
  for( int j = 1; i <=n; ++i)
     fact = fact * j;
  e += 1/(float)fact;
}

There is a better way to get the factorial in constant time... but I ca't remember it.

 

[prosper]

//correct me if I am wrong
// The result e should be 2.5 if n=3
// There is little typing error in jstreich 's code
float e = 1.0f;
int n = 10;
for(int i = 1; i <= n; ++i)
{
  int fact = 1;
  for( int j = 1; j <=i; ++j)
     fact = fact * j;
  e += 1/(float)fact;
}

 

[juliam921]

float e = 1.0f;


What does the f do in the variable value above (1.0f)? Do you need it?

Thanks,
Julia

 

[prosper]

The f is needed.
float e = 1.0; This is invalid statement because Java thinks 1.0 is a double by default, so float e = 1.0f; will assign 1.0 float to e.

 

[jstreich]

Oh, I wasn't thinking about it as e, I was thinking about the harmonic series... 1/1, 1/2, 1/3, ..., with the factorial added.