A snail is at the bottom of a 6-foot well and wants to climb to the top. The snail can climb 3 feet while the sun is up, but slides down 1 foot at night while sleeping. The snail has a fatigue factor of 10%, which means that on each successive day the snail climbs 10%  3 = 0.3 feet less than it did the previous day. (The distance lost to fatigue is always 10% of the first day‘s climbing distance.) On what day does the snail leave the well, i.e., what is the first day during which the snail‘s height exceeds 6 feet? (A day consists of a period of sunlight followed by a period of darkness.) As you can see from the following table, the snail leaves the well during the third day.

Your job is to solve this problem in general. Depending on the parameters of the problem, the snail will eventually either leave the well or slide back to the bottom of the well. (In other words, the snail‘s height will exceed the height of the well or become negative.) You must find out which happens first and on what day.

Input 

The input file contains one or more test cases, each on a line by itself. Each line contains four integersH, U, D, and F, separated by a single space. If H = 0 it signals the end of the input; otherwise, all four numbers will be between 1 and 100, inclusive. H is the height of the well in feet, U is the distance in feet that the snail can climb during the day, D is the distance in feet that the snail slides down during the night, and F is the fatigue factor expressed as a percentage. The snail never climbs a negative distance. If the fatigue factor drops the snail‘s climbing distance below zero, the snail does not climb at all that day. Regardless of how far the snail climbed, it always slides D feet at night.

Output 

For each test case, output a line indicating whether the snail succeeded (left the well) or failed (slid back to the bottom) and on what day. Format the output exactly as shown in the example.

Sample Input 

6 3 1 10
10 2 1 50
50 5 3 14
50 6 4 1
50 6 3 1
1 1 1 1
0 0 0 0

Sample Output 

success on day 3
failure on day 4
failure on day 7
failure on day 68
success on day 20
failure on day 2

题目就是说有井里有一只蜗牛，白天爬上一段距离，晚上再滑落一段距离，蜗牛每天晚上滑落的距离不变，但是由于会疲劳，白天爬上的距离会越来越小，判断蜗牛最终能否成功爬出井口。

只要按照蜗牛爬行的过程模拟即可找到答案

WA过一次，因为忘记了蜗牛是不会向下爬的，当它疲劳到一定程度时，它白天就不再向上爬了。

 1 #include<iostream>
 2 #include<cstdio>
 3 
 4 using namespace std;
 5 
 6 int main()
 7 {
 8     double h, u, d, f;
 9     while (scanf ("%lf %lf %lf %lf", &h, &u, &d, &f) && h)
10     {
11         int day = 0;
12         double pos = 0, down = u * f / 100;
13         f /= 100;
14         while (true)
15         {
16             day++;
17             pos += u;
18             if (pos > h)
19                 break;
20             pos -= d;
21             if (pos < 0)
22                 break;
23             u -= down;
24             if(u<0)
25                 u=0;
26         }
27         if (pos > h)
28             printf ("success on day %d\n", day);
29         else if (pos < 0)
30             printf ("failure on day %d\n", day);
31     }
32     return 0;
33 }

[C++]

UVa 573 The Snail