C program to calculate factorial of a number

Calculating the factorial of a number is a common task in computer programming and mathematics. The factorial of a non-negative integer n is the product of all positive integers less than or equal to n. It is denoted by n!. This article will guide you through writing a C program to calculate the factorial of a given number, providing a detailed explanation and sample code.

Understanding Factorials

The factorial of a number n is defined as:

n! = n x (n-1) x (n-2) x … x 1

For example:

• 5!=54321=120
• 3!=321=6
• 0!=1 (by definition)

Steps to Calculate Factorial

1. Input the Number: Read the number from the user.
2. Initialize the Result: Start with a result variable set to 1.
3. Loop through Numbers: Multiply the result by each number from 1 to n.
4. Output the Result: Print the calculated factorial.

Write a C program to calculate factorial of a number

Here is a C program to calculate the factorial of a given number:

#include <stdio.h>

int main() {
    int number;
    unsigned long long result = 1;

    // Input the number
    printf("Enter a non-negative integer: ");
    scanf("%d", &number);

    // Calculate factorial
    for (int i = 1; i <= number; ++i) {
        result *= i;
    }

    // Output the result
    printf("Factorial of %d is %llu", number, result);

    return 0;
}

Output

Enter a non-negative integer: 5
Factorial of 5 is 120

Explanation

1. Input the Number:
   • The program prompts the user to enter a non-negative integer using printf.
   • The number is read using scanf and stored in the variable number.
2. Initialize the Result:
   • The variable result is initialized to 1. This will hold the product of numbers as we compute the factorial.
3. Calculate the Factorial:
   • A for loop is used to multiply result by each number from 1 to number.
   • The loop runs number times, and in each iteration, result is updated with the product of result and the current value of i.
4. Output the Result:
   • After the loop completes, the program prints the calculated factorial using printf.

Example

For an input of 5, the program will:

• Initialize result to 1.
• Multiply result by each number from 1 to 5:
  • 1*1=1
  • 1*2=2
  • 2*3=6
  • 6*4=24
  • 24*5=120
• Print Factorial of 5 is 120.