source code name: discount.C

void main()
{
int qty,rt,amt,amtpaid;
int dis=0;
clrscr();
printf(" enter quantity and rate of items: \n");
scanf("%d%d",&qty,&rt);
amt=qty*rt;
if(amt>=1000)
dis=amt*0.1;
else
printf("\n sorry no discount , purchase some items ");
amtpaid=amt-dis;

printf(" \n actually paid amount=%d  &  discount gained = %d ",amtpaid, dis);
getch();
}

output:

1)  enter quantity and rate of items: 100 25

actually paid amount=2250  &  discount gained =250

2) enter quantity and rate of items: 20 40

 sorry no discount , purchase some items

 actually paid amount=800  &  discount gained =0