How can i make this code to give output sum of the Nth term of the series. EXAMPLE : input:2 ,output=-1, Input:3, output=2,

Question

#include <stdio.h>
int main ()
{
int n, i,v=1,dif;
printf("Enter Value: ");
scanf("%d", &n);

{
printf("Result: ");
for (i = 1; i < n; i++)
{

printf("%d,",i*v);
v=v*-1;

}

printf("%d", i*v);

}
return 0;
}

Need the sum of this series

Answer 1

/*
Siyam without loop (most efficient):
https://code.sololearn.com/c3w78zdmZ0q4/?ref=app
*/

// sum of even numbers up to n:

int m = n/2;
int e = m*(m+1);

// sum of odd numbers up to n:

int o = m+(n&1);
o = o*o;

// sum of nth term of serie:

int s = o-e;

Answer 2

Here
https://code.sololearn.com/c96HDh3Dcd0z/?ref=app
This may help you
If you want to print only sum of series and not series itself then remove 'printf("%d", i*v)' from code.