# Find the Sum of the series 1/2 – 2/3 + 3/4 – 4/5 + … till N terms

Given a number N, the task is to find the sum of the below series till N terms. Examples:

Input: N = 6
Output: -0.240476

Input: N = 10
Output: -0.263456

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach: From the given series, find the formula for Nth term:

1st term = 1/2
2nd term = - 2/3
3rd term = 3/4
4th term = - 4/5
.
.
Nthe term = ((-1)N) * (N / (N + 1))


Therefore:

Nth term of the series Then iterate over numbers in the range [1, N] to find all the terms using the above formula and compute their sum.

Below is the implementation of the above approach:

## C++

 // C++ program for the above approach     #include  using namespace std;     // Function to find the sum of series  void printSeriesSum(int N)  {      double sum = 0;         for (int i = 1; i <= N; i++) {             // Generate the ith term and          // add it to the sum if i is          // even and subtract if i is          // odd          if (i & 1) {              sum += (double)i / (i + 1);          }          else {              sum -= (double)i / (i + 1);          }      }         // Print the sum      cout << sum << endl;  }     // Driver Code  int main()  {      int N = 10;         printSeriesSum(N);      return 0;  }

## Java

 // Java program for the above approach  class GFG{      // Function to find the sum of series  static void printSeriesSum(int N)  {      double sum = 0;          for (int i = 1; i <= N; i++) {              // Generate the ith term and          // add it to the sum if i is          // even and subtract if i is          // odd          if (i % 2 == 1) {              sum += (double)i / (i + 1);          }          else {              sum -= (double)i / (i + 1);          }      }          // Print the sum      System.out.print(sum +"\n");  }      // Driver Code  public static void main(String[] args)  {      int N = 10;          printSeriesSum(N);  }  }     // This code is contributed by 29AjayKumar

## Python3

 # Python3 program for the above approach     # Function to find the sum of series  def printSeriesSum(N) :             sum = 0;         for i in range(1, N + 1) :             # Generate the ith term and          # add it to the sum if i is          # even and subtract if i is          # odd          if (i & 1) :              sum += i / (i + 1);                  else :              sum -= i / (i + 1);                # Print the sum      print(sum);     # Driver Code  if __name__ == "__main__" :         N = 10;         printSeriesSum(N);            # This code is contributed by Yash_R

## C#

 // C# program for the above approach  using System;      class GFG {          // Function to find the sum of series  static void printSeriesSum(int N)  {      double sum = 0;         for (int i = 1; i <= N; i++) {             // Generate the ith term and          // add it to the sum if i is          // even and subtract if i is          // odd          if ((i & 1)==0) {              sum += (double)i / (i + 1);          }          else {              sum -= (double)i / (i + 1);          }      }         // Print the sum      Console.WriteLine(sum);  }     // Driver Code      public static void Main (string[] args)      {                int N = 10;         printSeriesSum(N);  }  }     // This code is contributed by shivanisinghss2110

Output:

-0.263456


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