Q. Sum of Arthimetric Progression ?

THE OUTPUT WOULD BE

 
#include<stdio.h>
#include<conio.h>
  void main( )
  {    clrscr( );
        int Sn,a,n,d;
        printf("Enter first term=");
        scanf("%d",&a);
        printf("Enter difference=");
        scanf("%d",&d);
        printf("Enter \'n\' terms=");
        scanf("%d",&n);
        Sn=n/2*(2*a+(n-1)*d);
        printf("Sum of nth term =%d",Sn);
        getch( );
}