程序为什么错误

#include<cstdio>
int main()
{ int n;
  float b=0,c=0,d=0,e=0;
  scanf("%d",&n);
  int a[n+1];
  for(int i=1;i<=n;++i)
     scanf("%d",a[i]);
  for(int i=1;i<=n;++i)
  {
      if((0<=a[i])and(a[i]<=18))
        b+=1;
      else if((19<=a[i])and(a[i]<=35))
        c+=1;
      else if((36<=a[i])and(a[i]<=60))
      d+=1;
    else if(61<=a[i])
      e+=1;   
  }
  b/=n;
  c/=n;
  d/=n;
  e/=n;
  printf("%.2f %.2f %.2f %.2f",b,c,d,e);
  return 0;

}