SUM OF THE SERIES 1+2+3+---------+n

#include<stdio.h>

#include<conio.h>

void main()

{

  int r;

  clrscr();

  printf("\nEnter the number range: ");

  scanf("%d",&r);

  printf("\nSum of the series is: %d",(r*(r+1))/2);

  getch();

}