Series 1-3+5-7+9-11 .....

/*    1-3+5-7+9-11 ..... */

#include<stdio.h>

#include<conio.h>

void main()

{

int i, n, sum=0,k=-1;

clrscr();

printf("\n Enter the no.of terms: ");

scanf("%d",&n);

for(i=1;i<=2*n;i=i+2)

{

k=-k;

sum= sum + (k*i);

}

printf("\n Sum of %d terms: %d", n, sum);

getch();

}