CODEWITHSUNDEEP
cfactorial
Tanmay Kajbaje
Tanmay Kajbaje

Reputation: 61

Number of Trailing Zeros in a Factorial in c

I am new to C programming I want to find out the number of trailing zeros in a Factorial of given number 

{
        long int n=0,facto=1,ln=0;
        int zcount=0,i=1;
        printf("Enter a number:");
        scanf("%ld",&n);
        if(n==0)
        {
          facto=1;
        }
        else
        {
           for(i=1;i<=n;i++)
           {
              facto=facto*i;
           }
        }
        printf("%ld",facto);
        while(facto>0)
        {
           ln=facto%10;
           facto/10;
           if(ln=!0)
           { 
               break;
           }
           else
           { 
               zcount+=1;
           }
        }
        printf("Tere are Total %d Trailing zeros in given factorial",zcount);
}

I have tried to calculate the modulo of the the number which will return the last digit of given number as the remainder and then n/10; will remove the last number.

After executing the program the output always shows number of trailing zeros as "0",The condition if(ln =! 0) always gets satisfied even if there is a zero.

Upvotes: 1

Views: 8761

Answers (7)

Fahim A R Akil
Fahim A R Akil

Reputation: 31

I have solved this kind of problem, I think your question is just find the number of trailing zeros of a factorial number like - 15! = 1307674368000 if you look at the trailing 3 digits which are 000 Efficient code is


  int n;cin>>n; 
  int ans = 0;
   while(n)
   { ans += (n = n/5);}
   cout<<ans;

Here one should look for int overflow, array bounds. Also, the special cases are n=1?

Upvotes: 0

Noor A Shuvo
Noor A Shuvo

Reputation: 2817

Try this

int trailingZeroCountInFactorial(int n)
{
  int result = 0;
  for (int i = 5; i <= n; i *= 5)
  {
    result += n / i;
  }
  return result;
}

To learn, how it works, there is a great explanation here

Upvotes: 0

user6228199
user6228199

Reputation: 1

package lb;

import java.util.Scanner;

public class l1 {

public static void main(String[] args) {
    // TODO Auto-generated method stub
    Scanner s=new Scanner(System.in);
    int n=s.nextInt();
    int a=n/5;
        if(a<5)
        {
        System.out.println(a);
        }
        else
        {
        int c=a/5+a;
        System.out.println(c);
        }
    }
}

Upvotes: 0

Nikerboker
Nikerboker

Reputation: 843

Let us remember math (wiki):

int trailingZeroCountInFactorial(int n)
{
  int result = 0;
  for (int i = 5; i <= n; i *= 5)
  {
    result += n / i;
    if(i > INT_MAX / 5) // prevent integer overflow
      break;
  }
  return result;
}

Upvotes: 5

Arpit Parmar
Arpit Parmar

Reputation: 300

{

long int n=0,facto=1,ln=0;
int zcount=0,i=1;
printf("Enter a number:");
scanf("%ld",&n);
if(n==0)
{
  facto=1;
}
else
{
   for(i=1;i<=n;i++)
   {
      facto=facto*i;
   }
}
printf("%ld\n",facto);
while(facto>0)
{
   ln=(facto%10);
   facto/=10;  //here you done one mistake
   if(ln!=0)   //another one here
   {
       break;
   }
   else
   {
       zcount+=1;
   }
}
printf("Tere are Total %d Trailing zeros in given factorial",zcount);

} /Run this code it will work now and mistakes you already knows i guess/

Upvotes: -2

Nishant
Nishant

Reputation: 2619

The correct syntax in

if(ln!=0) 
{ 
    // do something     
}

In if ( ln=!0 ) , first !0 is evaluated then = assigns !0(which is 1) to ln, then if checks the value of ln, if the value is non-zero(in this case it is 1 due to previous assignment) then break statement is executed.

Also, this approach will not work for numbers larger than 25. It is obvious that the power of 5 in n! will be the answer.

The following expression gives the power of a prime p in n! :- f(n/p) + f(n/p^2) + f(n/p^3) + ..... (until f(n/p^k) return zero, where f(a) returns the greatest integer of a or the floor of a

Upvotes: 0

Iharob Al Asimi
Iharob Al Asimi

Reputation: 53026

This

if(ln=!0)

means ln = !0 i.e. you are assigning !0 to ln so the condition is always true, change it to

if (ln != 0)

you can use an assignment as a truth value, but if you are sure you are doing it.

To prevent accidentally doing it, turn on compiler warnings.

Upvotes: 1

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