filewrite using structure

#include
#include
calc(struct salesdata *salesptr);
struct salesdata{
		char transno[4];
		int salesno;
		int prodno;
		int unit_sold;
		float value_of_sale;
		};
void main()
{

FILE *fp;
struct salesdata salesrec,*ptr;
clrscr();
ptr=fopen("rand.txt","w");
printf("Enter transsaction no: ");
scanf("%3s",salesrec.transno);
fflush(stdin);

printf("Enter salesman no: ");
scanf("%d",&salesrec.salesno);
fflush(stdin);

printf("Enter the product number: ");
scanf("%d",&salesrec.prodno);
fflush(stdin);

printf("Enter unit sold: ");
scanf("%d",&salesrec.unit_sold);
fflush(stdin);

(float)salesrec.value_of_sale=calc(&salesrec);
printf("Value of sale: %f");

ptr=&salesrec;
fwrite(ptr, sizeof(struct salesdata),1,fp);


getch();
}
calc(struct salesdata *salesptr)
{
static float prod_rate[4]={ 12.0, 65.0, 30.0, 20.5 };
salesptr->value_of_sale=(float)salesptr->unit_sold* prod_rate[salesptr->prodno-1];
return salesptr->value_of_sale;
}