UVa 369 combinations: How to use double to combine numbers

369-combinations

Time limit:3.000 seconds

Http://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&category=24&page=show_problem &problem=305

Computing the exact number of ways that N things can is taken m at a time can is a great challenge when nand/or M become v ery large. Challenges are the stuff of contests. Therefore, you are to make just such a computation given the following:

GIVEN:

Compute the EXACT value of:

You may assume that final value of C would fit in a 32-bit Pascal longint or a C long.

For the record, the exact value of 100! is:

     93,326,215,443,944,152,681,699,238,856,266,700,490,715,968,264,381,621,
        468,592,963,895,217,599,993,229,915,608,941,463,976,156,518,286,253,
        697,920,827,223,758,251,185,210,916,864,000,000,000,000,000,000,000,000

Input and Output

This article URL address: http://www.bianceng.cn/Programming/sjjg/201410/45361.htm

The input to this program would be one or more lines each containing zero or more leading spaces, a value forn, one or more Spaces, and a value for M. The last line of the input file would contain a dummy N, M pair with both values equal to zero. Your program should terminate "when this" is read.

The output from this program should is in the form:

N things taken M at a time is C exactly.

Sample Input

       6  5  6
       0  0

Sample Output

Things taken 6 at A/A is 1192052400 exactly.
Things taken 5 at A/A is 15504 exactly.
Things taken 6 at A/A is 18564 exactly.

Note this sentence:

"You may assume that final value of C would fit in a 32-bit Pascal longint or a C long."

Complete code:

/*0.022s*/
     
#include <cstdio>  
     
int main ()  
{  
    int N, M, I;  
    Double C;  
    while (scanf ("%d%d", &n, &m), N)  
    {  
        C = 1.0;  
        for (i = N; i > N-m-I.) C *= (double) I;  
        for (i = 2; I <= M ++i) C/= (double) I;  
        printf ("%d things taken%d at a time is%.0f exactly.\n", N, M, C);  
    return 0;  
}