Find Factorial of a Number

#include <stdio.h>

int main() {
    int number, i;
    unsigned long long factorial = 1;  // Use unsigned long long for large results

    // Asking the user to input a positive integer
    printf("Enter a positive integer: ");
    scanf("%d", &number);

    // Factorial of negative numbers doesn't exist
    if (number < 0) {
        printf("Factorial of a negative number doesn't exist.\n");
    } else {
        // Calculating factorial
        for (i = 1; i <= number; ++i) {
            factorial *= i;  // Multiply factorial by i
        }
        // Output the result
        printf("Factorial of %d = %llu\n", number, factorial);
    }

    return 0;
}

Explanation:

Returning 0: The program returns 0 to indicate successful execution.cCopy codereturn 0;

Including the standard input-output library: We include the stdio.h header file so we can use printf for output and scanf for input.cCopy code#include <stdio.h>

Main function: The program execution begins with the main() function.cCopy codeint main() { ... }

Declaring variables:

• number stores the input number.
• i is the loop counter used to calculate the factorial.
• factorial is initialized to 1 and is used to store the result of the factorial calculation. We use unsigned long long because the factorial of larger numbers can get very large quickly.

User input: We prompt the user to input a positive integer using printf, and scanf stores the number in the number variable.cCopy codeprintf("Enter a positive integer: "); scanf("%d", &number);

Checking for negative input: Factorial is not defined for negative numbers. If the user inputs a negative number, the program prints an error message.cCopy codeif (number < 0) { printf("Factorial of a negative number doesn't exist.\n"); }

Calculating the factorial:

• If the input is a positive number or zero (because the factorial of 0 is 1), the program uses a for loop to multiply numbers from 1 to the input number.
• For example, if the user enters 5, the loop will perform: 1 * 2 * 3 * 4 * 5, and store the result in factorial.

Displaying the result: After calculating the factorial, the program prints the result using printf. The format specifier %llu is used to print an unsigned long long integer.cCopy codeprintf("Factorial of %d = %llu\n", number, factorial);

OUTPUT

Enter a positive integer: 5
Factorial of 5 = 120

Enter a positive integer: 0
Factorial of 0 = 1

Enter a positive integer: -3
Factorial of a negative number doesn’t exist.

Summary:

This program checks for negative input, calculates the factorial using a loop, and handles large numbers using unsigned long long.

The factorial of a number is the product of all positive integers from 1 to that number.

For example, the factorial of 5 is 5! = 5 * 4 * 3 * 2 * 1 = 120.