# Java Program to Find Factorial of a Number

#### In this program, you’ll learn to find the factorial of a number using for and while loop in Java.

The factorial of a positive number `n` is given by:

factorial of n (n!) = 1 * 2 * 3 * 4 * ... * n

## Example 1: Find Factorial of a number using for loop

```
public class Factorial{
public static void main(String[] args){
int num = 10;
long factorial = 1;
for(int i = 1; i <= num; ++i)
{
// factorial = factorial * i;
factorial *= i;
}
System.out.printf("Factorial of %d = %d", num, factorial);
}
}
```

**Output**

Factorial of 10 = 3628800

In this program, we’ve used for loop to loop through all numbers between 1 and the given number `num` (10), and the product of each number till `num` is stored in a variable `factorial`.

We’ve used `long` instead of `int` to store large results of factorial. However, it’s still not big enough to store the value of bigger numbers (say 100).

For results that cannot be stored in a long variable, we use `BigInteger`

variable declared in `java.math`

library.

## Example 2: Find Factorial of a number using BigInteger

```
import java.math.BigInteger;
public class Factorial{
public static void main(String[] args){
int num = 30;
BigInteger factorial = BigInteger.ONE;
for(int i = 1; i <= num; ++i)
{
// factorial = factorial * i;
factorial = factorial.multiply(BigInteger.valueOf(i));
}
System.out.printf("Factorial of %d = %d", num, factorial);
}
}
```

**Output**

Factorial of 30 = 265252859812191058636308480000000

Here, instead of `long`

, we use `BigInteger`

variable factorial.

Since, `*`

cannot be used with `BigInteger`

, we instead use `multiply()`

for the product. Also, `num` should be casted to `BigInteger`

for multiplication.

Likewise, we can also use a while loop to solve this problem.

## Example 3: Find Factorial of a number using while loop

```
public class Factorial{
public static void main(String[] args){
int num = 5, i = 1;
long factorial = 1;
while(i <= num)
{
factorial *= i;
i++;
}
System.out.printf("Factorial of %d = %d", num, factorial);
}
}
```

**Output**

Factorial of 5 = 120

In the above program, unlike a for loop, we have to increment the value of `i` inside the body of the loop.

Though both programs are technically correct, it is better to use for loop in this case. It’s because the number of iteration (upto `num`) is known.

# Python Example for Beginners

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There are two sides to machine learning:

**Practical Machine Learning:**This is about querying databases, cleaning data, writing scripts to transform data and gluing algorithm and libraries together and writing custom code to squeeze reliable answers from data to satisfy difficult and ill defined questions. It’s the mess of reality.**Theoretical Machine Learning**: This is about math and abstraction and idealized scenarios and limits and beauty and informing what is possible. It is a whole lot neater and cleaner and removed from the mess of reality.

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