A Simple Question of Chemistry

#include<stdio.h>
int main()
{
int i, l;
 double a[];
double b[];
 l = ;
 while(scanf("%lf", &a[l]) && a[l] != )
{
l++;
 }
for(i=; a[i]!= && i<l; i++)
printf("%.2lf\n",a[i]-a[i-]);
 printf("End of Output\n");
return ;
}