/* Sum of series - Program to calculate sum of series 1 - x^2/2! + x^4/4! - x^6/6! + x^8/8! - ... */

#include  <stdio.h>
#include  <math.h>
#include  <conio.h>

long  fact(int  n) ;

void  main()
{
    int  i, k, n ;
    float  x, sum=0 ;
    clrscr() ;
    printf("Enter the number of terms: ") ;
    scanf("%d", &n) ;
    printf("Enter the value of x: ") ;
    scanf("%f", &x) ;
    /* i keeps track of term count , whereas k is used for calculation purpose */
    for(i=1, k=0 ; i<=n ; i++, k=k+2)
        {
            if(i%2==1)
                sum = sum + pow(x,k)/fact(k) ;
            else
                sum = sum - pow(x,k)/fact(k) ;
        }
    printf("Sum of the required series is %f", sum) ;
    getch() ;
}

long fact(int  n)
{
    int  i ;
    long f=1;
    for(i=1 ; i<=n ; i++)
        f=f*i ;
    return  f ;
}

/*
Output1 :

Enter the number of terms: 1
Enter the value of x: 8
Sum of the required series is 1.000000

Output2:

Enter the number of terms: 4
Enter the value of x: 2
Sum of the required series is -0.422222

Output3:

Enter the number of terms: 3
Enter the value of x: 5
Sum of the required series is 14.541667
*/