C Exercises: Find the number of trailing zeroes in a given factorial

Last update on August 07 2025 12:49:20 (UTC/GMT +8 hours)

10. Trailing Zeros in Factorial Variants

Write a C program to find the number of trailing zeroes in a given factorial.

Example 1:
Input: 4
Output: 0
Explanation: 4! = 24, no trailing zero.
Example 2:
Input: 6
Output: 1
Explanation: 6! = 720, one trailing zero.

Example:
Input:
n = 4
n = 5
Output:
Number of trailing zeroes of factorial 4 is 0
Number of trailing zeroes of factorial 5 is 1

Visual Presentation:

Sample Solution:

C Code:

#include <stdio.h>

// Function to count the number of trailing zeroes in the factorial of a number
static int trailing_Zeroes(int n) {
    int number = 0;

    // Loop to calculate the number of trailing zeroes
    while (n > 0) {
        number += n / 5; // Count how many multiples of 5 are present in the factorial
        n /= 5; // Divide the number by 5 to check for the next multiple of 5
    }

    return number; // Return the count of trailing zeroes
}

// Main function to test the trailing_Zeroes function with different values
int main(void) {
    int n = 4;
    printf("\nNumber of trailing zeroes of factorial %d is %d ", n, trailing_Zeroes(n)); // Display the number of trailing zeroes for n
    n = 5;
    printf("\nNumber of trailing zeroes of factorial %d is %d ", n, trailing_Zeroes(n)); // Display the number of trailing zeroes for n
    return 0;
}

Sample Output:

Number of trailing zeroes of factorial 4 is 0 
Number of trailing zeroes of factorial 5 is 1 

Flowchart:

For more Practice: Solve these Related Problems:

• Write a C program to calculate the number of trailing zeros in n! by counting factors of 5.
• Write a C program to compute trailing zeros in a factorial using iterative division by powers of 5.
• Write a C program to find trailing zeros in large factorials by optimizing the factor counting process.
• Write a C program to display both the factorial value (if small) and its trailing zero count for comparison.

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