c - Sum of the all the numbers between a and b -

i need create program gives sum of numbers between constants of a , b given user. b needs greater a.

#include <stdio.h>  void main() {     int index, begno, endno, sum = 0;     printf("program sum of numbers in given range\n");      printf("enter beg. no.: ");     scanf("%d", &begno);     printf("enter end. no.: ");     scanf("%d", &endno);     index = begno;      for(; index <= endno; index ++)         sum = sum + index;      printf("the sum of numbers between %d , %d is: %d", begno, endno, sum); } 

the code given looks ok, if want sum without including last number, case should change loop this

for(; index < endno; index ++)