OJ Board

Why WA?
#include<stdio.h>
#include<math.h>

int main()
{
int i;
int a;
double b,c,d;
double u,v,ac,s,t;
for(i=1;; i++)
{
scanf("%d",&a);
if(a==0)break;
scanf("%lf %lf %lf",&b,&c,&d);

printf("Case %d: ",i);

if(a==1)
{
u=b;
v=c;
t=d;
ac=(v-u)/t;
s=u*t+.5*ac*t*t;
printf("%.3lf ...