Efficient program to calculate e^x

The value of Exponential Function e^x can be expressed using following Taylor Series.

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

How to efficiently calculate the sum of above series? 
The series can be re-written as 
 

e^x = 1 + (x/1) (1 + (x/2) (1 + (x/3) (........) ) ) 

Let the sum needs to be calculated for n terms, we can calculate sum using following loop.

for (i = n - 1, sum = 1; i > 0; --i )
 sum = 1 + x * sum / i; 

Following is implementation of the above idea. 
 

Output: 

e^x = 2.718282

Time Complexity: O(n)

Auxiliary Space: O(1), since no extra space has been taken.

This article is compiled by Rahul and reviewed by GeeksforGeeks team.