Factorial

README.md

@@ -9,11 +9,14 @@
   * [Streaming operators](#streaming-operators)
 * [Methods](#methods)
   * [clear](#clear)
-  * [to_string](#toString)
   * [abs](#abs)
-  * [pow](#pown)
+  * [pow](#powint)
   * [digits](#digits)
-  * [trailing_zeros](#trailingZeros)
+  * [trailing_zeros](#trailing_zeros)
+* [Functions](#functions)
+  * [abs](#absbigint)
+  * [to_string](#to_stringbigint)
+  * [factorial](#factorialint)
 
 #Description
 Bigint class provides math operations for arbitrarily large numbers. You know the limit is reached when your computer freezes.
@@ -79,20 +82,13 @@ cout << a.pow(486);;  //1459889316343...
 a.clear();
 cout << a; //0
 ```
-##to_string()
-Convers Dodecahedron::Bigint to a string.
-```C++
-string str;
-Dodecahedron::Bigint a = 4558;
-str = a.pow(486).to_string();
-```
 ##abs()
 Absolute value.
 ```C++
 Dodecahedron::Bigint a = -4558;
 cout << a.abs() // 4558
 ```
-##pow(n)
+##pow(int)
 Raises to the power of N.
 ```C++
 Dodecahedron::Bigint a = 4558;
@@ -111,4 +107,23 @@ Returns the number of trailing zeros.
 Dodecahedron::Bigint a = 4558;
 a.pow(486);
 cout << a.trailing_zeros(); //972
+```
+#Functions
+##abs(Bigint)
+Same as [abs](#abs), but returns a new instance;
+```C++
+Dodecahedron::Bigint a = -455897864531248;
+cout << abs(a) // 455897864531248
+```
+##to_string(Bigint)
+Converts the big integer to a string.
+```C++
+string str;
+Dodecahedron::Bigint a = 455897864531248;
+str = to_string(a);
+```
+##factorial(int)
+Returns a factorial of an integer, aka n!
+```C++
+cout << Dodecahedron::factorial(a); //70`000+ digit number
 ```

bigint.cpp

@@ -230,7 +230,7 @@ namespace Dodecahedron {
 
 	//Access
 	int Bigint::operator[](int const &b)  {
-		return to_string()[b]-'0';
+		return to_string(*this)[b]-'0';
 	}
 
 	//Trivia
@@ -264,11 +264,6 @@ namespace Dodecahedron {
 		positive = true;
 		skip = 0;
 	}
-	std::string Bigint::to_string() {
-		std::ostringstream stream;
-		stream << *this;
-		return stream.str();
-	}
 	Bigint& Bigint::abs() {
 		positive = true;
 		return *this;
@@ -322,4 +317,22 @@ namespace Dodecahedron {
 	Bigint abs(Bigint value) {
 		return value.abs();
 	}
+	std::string to_string(Bigint value) {
+		std::ostringstream stream;
+		stream << value;
+		return stream.str();
+	}
+	Bigint factorial(int n) {
+		Bigint result = 1;
+		if(n % 2) {
+			result = n;
+			n--;
+		}
+		int last = 0;
+		for(; n >= 2; n -= 2) {
+			result *= n+last;
+			last += n;
+		}
+		return result;
+	}
 }

bigint.h

@@ -52,7 +52,6 @@ namespace Dodecahedron {
 
 		//Helpers
 		void clear();
-		std::string to_string();
 		Bigint& abs();
 
 		//Power
@@ -66,6 +65,8 @@ namespace Dodecahedron {
 		int compare(Bigint const &b) const; //0 a == b, -1 a < b, 1 a > b
 	};
 	Bigint abs(Bigint value);
+	std::string to_string(Bigint value);
+	Bigint factorial(int n);
 }
 
 #endif