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

## C For Loop: Exercise-18 with Solution

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

**Sample Solution:**

**C Code:**

```
#include <stdio.h> // Include the standard input/output header file.
int main() {
float x, sum, t, d; // Declare variables to store input and intermediate values.
int i, n; // Declare variables for loop control and input.
// Prompt the user to input the value of 'x'.
printf("Input the Value of x :");
scanf("%f", &x); // Read the value of 'x' from the user.
// Prompt the user to input the number of terms.
printf("Input the number of terms : ");
scanf("%d", &n); // Read the value of 'n' from the user.
sum = 1; // Initialize 'sum' to 1, as the first term is always 1.
t = 1; // Initialize 't' to 1 for the first term.
// Loop to calculate the sum of the series.
for (i = 1; i < n; i++) {
d = (2 * i) * (2 * i - 1); // Calculate the denominator for the term.
t = -t * x * x / d; // Calculate the term value.
sum = sum + t; // Add the term to the sum.
}
// Print the final result along with the input values.
printf("\nThe sum = %f\nNumber of terms = %d\nValue of x = %f\n", sum, n, x);
return 0; // Return 0 to indicate successful execution.
}
```

**Flowchart: **

or

```
#include <stdio.h>
int main()
{
// Variable declaration
float x, s, t, num = 1.00, fac = 1.00;
int i, n, pr, y = 2, m = 1;
// User input for x and the number of terms
printf("Input the Value of x: ");
scanf("%f", &x);
printf("Input the number of terms: ");
scanf("%d", &n);
// Initializing variables for summation
s = 1.00;
t = 1.00;
// Loop to calculate the sum based on the number of terms
for (i = 1; i < n; i++)
{
// Loop to calculate factorial and power of x
for (pr = 1; pr <= y; pr++)
{
fac = fac * pr; // Calculate factorial
num = num * x; // Calculate power of x
}
m = m * (-1); // Alternate the sign for the power of x
num = num * m; // Applying the alternating sign
t = num / fac; // Calculate the term value for this iteration
s = s + t; // Add the term value to the sum
y = y + 2; // Increment for the next odd number (power of x)
num = 1.00; // Resetting num for the next iteration
fac = 1.00; // Resetting fac for the next iteration
}
// Output the result
printf("\nThe sum = %f\nNumber of terms = %d\nValue of x = %f\n", s, n, x);
return 0;
}
```

Sample Output:

Input the Value of x :2 Input the number of terms : 5 the sum = -0.415873 Number of terms = 5 value of x = 2.000000

**Flowchart: **

**C Programming Code Editor:**

**Previous:** Write a program in C to make such a pattern like a pyramid with a number which will repeat the number in the same row.

**Next:** Write a program in C to display the n terms of harmonic series and their sum.

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