# Perl | Math::BigInt->bfac() method

`Math::BigInt` module in Perl provides objects that represent integers with arbitrary precision and overloaded arithmetical operators.

`bfac()` method of `Math::BigInt` module is used to calculate factorial of a number stored as `BigInt` object.

Syntax: Math::BigInt->bfac()

Parameter: None

Returns: a normalised BigInt object whose value represents the factorial of the given number.

Example 1: Use of `Math::BigInt->bfac()` method

 `#!/usr/bin/perl  ` ` `  `# Import Math::BigInt module ` `use` `Math::BigInt; ` ` `  `\$num` `= 5; ` ` `  `# Calculate the factorial of ` `# the above specified number ` ` `  `# Create a BigInt object ` `\$x` `= Math::BigInt->new(``\$num``); ` ` `  `# Use Math::BigInt->bfac() method ` `# to calculate factorial ` `\$factorial` `= ``\$x``->bfac(); ` ` `  `print` `"Factorial of \$num : \$factorial\n"``; ` ` `  ` `  `\$num` `= 10; ` ` `  `# Calculate the factorial of ` `# the above specified number ` ` `  `# Create a BigInt object ` `\$x` `= Math::BigInt->new(``\$num``); ` ` `  `# Use Math::BigInt->bfac() method ` `# to calculate factorial ` `\$factorial` `= ``\$x``->bfac(); ` ` `  `print` `"Factorial of \$num : \$factorial\n"``; `

Output:

```Factorial of 5 : 120
Factorial of 10 : 3628800
```

Example 2: Use of `Math::BigInt->digit()` method to count digits in factorial of big numbers

 `#!/usr/bin/perl  ` ` `  `# Import Math::BigInt module ` `use` `Math::BigInt; ` ` `  `\$num` `= 100; ` ` `  `# Calculate the factorial of ` `# the above specified number ` ` `  `# Create a BigInt object ` `\$x` `= Math::BigInt->new(``\$num``); ` ` `  `# Use Math::BigInt->bfac() method ` `# to calculate factorial ` `\$factorial` `= ``\$x``->bfac(); ` ` `  `# Print the factorial ` `print` `"Factorial of \$num : \$factorial \n"``; ` ` `  `# Print count of digits in factorial ` `\$count` `= ``\$factorial``->``length``(); ` `print` `"Count of digits in factorial : \$count"``; `

Output:

```factorial of 100 : 93326215443944152681699238856266700490715968264381621468592963895217599993229915608941463976156518286253697920827223758251185210916864000000000000000000000000
Count of digits in factorial : 158
```

Example 3: Use of `Math::BigInt->digit()` method to calculate value of nCr.

 `#!/usr/bin/perl  ` ` `  `# Import Math::BigInt module ` `use` `Math::BigInt; ` ` `  `# Value of n ` `\$n` `= 5; ` ` `  `# Value of r ` `\$r` `= 3; ` ` `  ` `  `# Create BigInt objects  ` `\$x` `= Math::BigInt->new(``\$n``); ` `\$y` `= Math::BigInt->new(``\$r``); ` `\$z` `= Math::BigInt->new(``\$n` `- ``\$r``); ` ` `  ` `  `# calculate nCr using  ` `# formula n! / (r! * (n-r)!) ` `\$nCr` `= ``\$x``->bfac() / (``\$y``->bfac() * ``\$z``->bfac()); ` ` `  ` `  `# Print calculated value of nCr ` `print` `"Value of \${n}C\${r} : \$nCr \n"``; ` ` `  ` `  `# Value of n ` `\$n` `= 50; ` ` `  `# Value of r ` `\$r` `= 15; ` ` `  ` `  `# Create BigInt objects  ` `\$x` `= Math::BigInt->new(``\$n``); ` `\$y` `= Math::BigInt->new(``\$r``); ` `\$z` `= Math::BigInt->new(``\$n` `- ``\$r``); ` ` `  ` `  `# calculate nCr using  ` `# formula n! / (r! * (n-r)!) ` `\$nCr` `= ``\$x``->bfac() / (``\$y``->bfac() * ``\$z``->bfac()); ` ` `  ` `  `# Print calculated value of nCr ` `print` `"Value of \${n}C\${r} : \$nCr \n"``; `

Output:

```Value of 5C3 : 10
Value of 50C15 : 2250829575120
```

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