sum_of_series.c

#include<stdio.h>
int main(){
    int i,n,c=1,sum=0;
    printf("\n Last number of series : ");
    scanf("%d",&n);
    if(n>0 && n%2){
        printf("\n Series = ");
        for(i=1; i<(n/2)+2; i++){
            if(i==1)printf("1");
            else printf(i%2?"+%d":"-%d",c);
            i%2 ? sum += c : (sum -= c);
            c+=2;
        }
        printf("\n\n Sum = %d\n",sum);
    }
    else
        printf("\n Number must be positive and odd\n");
    fflush(stdin);
    getch();
    return 0;
}