The factorial of a number is the product of all the numbers from 1 to that number. For example,
factorial of 5 is equal to 1 * 2 * 3 * 4 * 5 = 120.
The factorial of a positive number n is given by:
factorial of n (n!) = 1 * 2 * 3 * 4.....n
The factorial of negative numbers do not exist and the factorial of 0 is 1.
Example: Find Factorial Using Recursion
// program to find the factorial of a number
function factorial(x) {
// if number is 0
if (x == 0) {
return 1;
}
// if number is positive
else {
return x * factorial(x - 1);
}
}
// take input from the user
const num = prompt('Enter a positive number: ');
// calling factorial() if num is positive
if (num >= 0) {
const result = factorial(num);
console.log(`The factorial of ${num} is ${result}`);
}
else {
console.log('Enter a positive number.');
}
Output
Enter a positive number: 4 The factorial of 4 is 24
In the above program, the user is prompted to enter a number.
When the user enters a negative number, a message Enter a positive number. is shown.
When the user enters a positive number or 0, the function factorial(num)
gets called.
- If the user enters the number 0, the program will return 1.
- If the user enters a number greater than 0, the program will recursively call itself by decreasing the number.
- This process continues until the number becomes 1. Then when the number reaches 0, 1 is returned.
Here,
factorial(4) returns 4 * factorial(3) factorial(3) returns 4 * 3 * factorial(2) factorial(2) returns 4 * 3 * 2 * factorial(1) factorial(1) returns 4 * 3 * 2 * 1 * factorial(0) factorial(0) returns 4 * 3 * 2 * 1 * 1
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