# C#: Calculate the sum of the series [ 1-X^2/2!+X^4/4!- .........]

## C# Sharp For Loop: Exercise-18 with Solution

Write a program in C# Sharp to find the sum of the series [ 1-X^2/2!+X^4/4!- .........].

**Sample Solution**:

**C# Sharp Code:**

```
using System; // Importing necessary namespace
public class Exercise18 // Declaration of the Exercise18 class
{
public static void Main() // Main method, entry point of the program
{
double x, sum, t, d; // Declaration of variables of type double
int i, n; // Declaration of variables of type integer
Console.Write("\n\n"); // Displaying new lines
Console.Write("Calculate the sum of the series [ 1-X^2/2!+X^4/4!- .........]:\n"); // Displaying the purpose of the program
Console.Write("----------------------------------------------------------------"); // Displaying a separator
Console.Write("\n\n");
Console.Write("Input the Value of x :"); // Prompting the user to input the value of x
x = Convert.ToInt32(Console.ReadLine()); // Reading the value of x entered by the user
Console.Write("Input the number of terms : "); // Prompting the user to input the number of terms
n = Convert.ToInt32(Console.ReadLine()); // Reading the number of terms entered by the user
sum = 1; // Initializing the sum to 1 (as the series starts with 1)
t = 1; // Initializing t to 1 (initial term)
// Loop to calculate the sum of the series
for (i = 1; i < n; i++)
{
d = (2 * i) * (2 * i - 1); // Calculation of denominator value (factorial)
t = -t * x * x / d; // Calculation of the current term in the series
sum = sum + t; // Adding the current term to the sum
}
// Displaying the calculated sum, number of terms, and value of x
Console.Write("\nThe sum = {0}\nNumber of terms = {1}\nValue of x = {2}\n", sum, n, x);
}
}
```

Sample Output:

Calculate the sum of the series [ 1-X^2/2!+X^4/4!- .........]: ---------------------------------------------------------------- Input the Value of x :5 Input the number of terms : 2 the sum = -11.5 Number of terms = 2 value of x = 5

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