2-8

#include<stdio.h>
int main(void)
{
 int denominator,flag,i,n;
 double item,sum;

 printf("Enter n:");
 scanf("%d",&n);
 
 flag=1;
 denominator=1;
 sum=0;

 for(i=1;i<=n;i++){
  item=flag*1.0/denominator;
  sum=sum+item;
  flag=-flag;
  denominator=denominator+2;
 }
 printf("sum=%f\n",sum);

 return 0;
}