Va 10916 Factstone Benchmark (available for logarithm functions)

Factstone Benchmark
Amtel has announced that it will release a 128-bit computer chip by 2010, a 256-bit computer by 2020, and so on, continuing its strategy of doubling the word-size every ten years. (Amtel released a 64-bit computer in 2000, a 32-bit computer in 1990, a 16-bit computer in 1980, an 8-bit computer in 1970, and a 4-bit computer, its first, in 1960 .)
Amtel will use a new benchmark-the Factstone-to advertise the vastly improved capacity of its new chips. The Factstone rating is defined to be the largest integer n such that n! Can be represented as an unsigned integer in a computer word.

Given a year 1960 ≤ y ≤ 2160, what will be the Factstone rating of Amtel's most recently released chip?

There are several test cases. for each test case, there is one line of input containing y. A line containing 0 follows the last test case. for each test case, output a line giving the Factstone rating.

Sample Input
1960
1981
0 Output for Sample Input
3
8. The year is given. Each 10 years corresponds to a byte number supported by the current computer, and n is calculated! <Max (max is the maximum integer that can be expressed by the current computer), and returns the maximum n.
Solution: the number of bytes k = (year-1940)/10, the problem is converted to n! <2 ^ k <(n + 1 )!, If the simulation alone overflows, we take the same Logarithm for both sides, because log (a * B) = log (a) + log (B); so log (n !) = Sum (log (I), (1 <= I <= n), as long as the minimum sum (log (I)> k * log (2) is found ), the answer is I-1.

#include<stdio.h>#include<math.h>int main(){int year;while (scanf("%d", &year), year){int n = (year - 1940) / 10;double k = pow ( 2, n) * log10(2), sum = 0;for (int i = 1; ; i++){sum += log10(i);if (sum > k){printf("%d\n", i - 1);break;}}}return 0;}