input terminated by end of file 这个怎么实现？？ 请个为大虾指教!

用abort()函数退出，要含<cstdlib>,不知道对楼住来说有没有用

EOF判断文件尾

abort()和RUTURN 0有什么区别????

不知道是我对题目有什么误解，虽然做出来了，但总是提交不成功，不知道哪里出问题了，各位高手能不能帮我看看，感激涕流！！！！
　　　　题目如下

To calculate the circumference of a circle seems to be an easy task - provided you know its diameter. But what if you don't?

You are given the cartesian coordinates of three non-collinear points in the plane.
Your job is to calculate the circumference of the unique circle that intersects all three points.

Input Specification

The input file will contain one or more test cases. Each test case consists of one line containing six real numbers x₁,y₁, x₂,y₂,x₃,y₃, representing the coordinates of the three points. The diameter of the circle determined by the three points will never exceed a million. Input is terminated by end of file.

Output Specification

For each test case, print one line containing one real number telling the circumference of the circle determined by the three points. The circumference is to be printed accurately rounded to two decimals. The value of pi is approximately 3.141592653589793.

Sample Input

0.0 -0.5 0.5 0.0 0.0 0.5
0.0 0.0 0.0 1.0 1.0 1.0
5.0 5.0 5.0 7.0 4.0 6.0
0.0 0.0 -1.0 7.0 7.0 7.0
50.0 50.0 50.0 70.0 40.0 60.0
0.0 0.0 10.0 0.0 20.0 1.0
0.0 -500000.0 500000.0 0.0 0.0 500000.0

Sample Output

3.14
4.44
6.28
31.42
62.83
632.24
3141592.65

　题目的意思就是输入三个点坐标，求由这三个点组成的三角形的外接圆的周长．
希望各位能给点意见．万分感激！！！！！！！！！！！