Factorial Parsing

[Joes108]

Hi I need help writing this program

The factorial, n!, of an integer is defined to be:

n! = ( n * ( n - 1 ) * ( n - 2 ) * ….. * 2 * 1 )

An application of this formula is as follows, 5! = 5 * 4 * 3 * 2 * 1 = 120. This month’s challenge is to find the rightmost non-zero digit of n!. From the above example this number is 2. The rightmost non-zero digit of 12! ( 12! = 479001600 ) is 6.

Write a program that will input an integer between 1 and 14 inclusive and output the rightmost non-zero digit of the factorial. For an added challenge, handle inputs between 1 and 5000 inclusive.

Here are a few test cases for you to try:

Factorial Rightmost Non-Zero Digit
5 - 2
21 - 4
789 - 4
1000 - 2
4013 - 8



thanks for the help

[Hammer]

Show some code that you have written so far, and point out where you're having trouble, then someone will be able to help you better.

[Sang-drax]

Originally posted by Joes108
This month’s challenge is to find the rightmost non-zero digit of n!.

Haha, this is clearly some kind of contest or assignment.

But nevertheless:

cout << "Input n:";
int n,curr=1;
cin >> n;
for (int c=1; c<=n; ++c) 
{ 
    long tmp = c; 
    while (tmp%5 == 0) 
    { 
        tmp/= 5; 
        curr /=2; 
    } 
    curr = (curr % 100000) * tmp; 
} 
curr%=10;
cout << "Last number: " << curr;