Update README.md

Author: artemlos

README.md

@@ -2,7 +2,6 @@ Mathos Parser
 =============
 Mathos Parser (along with Mathos Parser Portable, and Expression Compiler) are currently transferred from CodePlex to GitHub. The old page can be found below:
 * http://mathosparser.codeplex.com/
-* 
 
 **Mathos Parser** is a mathematical expression parser, built on top of the .NET Framework, which allows you to parse all kinds of mathematical expressions, and in addition, add your own custom functions, operators, and variables (see the online demo).
 
@@ -22,6 +21,123 @@ NEW: We have launched a new support site, Q&A style: http://support.mathosprojec
 * And much more!
 
 ##Introduction
-Introduction
 
 Mathos Parser is a part of Mathos Project, a project that provides useful methods, structures, etc, to make the life a little bit easier! This math parser is fully independent of Mathos project, so you can just use this library to archive a powerful math parsing experience.
+
+##How to use
+
+It's really easy to use and understand this math parser. In this topic I will try to show you some (not all) key features of this library.
+
+* Adding a custom operator.
+* Adding a custom function.
+* Functions with more than one argument.
+* Programatically add variables.
+
+###Adding custom operator
+
+````
+// declaring the parser
+MathParser parser = new MathParser();
+
+//customize the operator list
+parser.OperatorList = new List<string>() { "^", "%", "*", ":", "/", "+", "-", ">", "<", "=" };
+
+// adding sqrt to the OperatorAction list
+parser.OperatorAction.Add("^", delegate(decimal numA, decimal numB)
+{
+    return (decimal)Math.Pow((double)numA, (double)numB);
+});
+
+// parsing and comparing
+Assert.IsTrue(parser.Parse("3^2") == (decimal)Math.Pow (3,2));
+````
+###Adding custom function
+````
+public void CustomFunctions()
+{
+    /*
+     * This test demonstrates three ways of adding a function
+     * to the Math Parser
+     * 
+     * 1) directly pointing to the function
+     * 2) lambda expression
+     * 3) anonymous method
+     */
+
+    MathParser parser = new MathParser();
+
+    //for long functions
+    parser.LocalFunctions.Add("numberTimesTwo", NumberTimesTwoCustomFunction); // adding the function
+    decimal resultA = parser.Parse("numberTimesTwo(3)");
+
+    //for short functions, use lambda expression, or anonymous method
+    // 1) using lambda epxression (recommended)
+    parser.LocalFunctions.Add("square", x => x[0] * x[0]);
+    decimal resultB = parser.Parse("square(4)");
+
+    // 2) using anonymous method
+    parser.LocalFunctions.Add("cube", delegate(decimal[] x)
+    {
+        return x[0] * x[0] * x[0];
+    });
+    decimal resultC = parser.Parse("cube(2)");
+
+}
+public decimal NumberTimesTwoCustomFunction(decimal[] input)
+{
+    return input[0] * 2;
+}
+````
+###Functions with more than one operator
+````
+/*
+ * This example demonstrates the "anonymous method" way of adding
+ * a function that can take more than one agument.
+ */
+
+ MathParser parser = new MathParser();
+
+//for long functions
+parser.LocalFunctions.Add("log", delegate(decimal[] input) // adding the function
+{
+    // input[0] is the number
+    // input[1] is the base
+
+  if (input.Length == 1)
+  {
+      return (decimal)Math.Log((double)input[0]);
+  }
+  else if (input.Length == 2)
+  {
+      return (decimal)Math.Log((double)input[0], (double)input[1]);
+  }
+  else
+  {
+      return 0; // false
+  }
+});
+
+decimal resultA = parser.Parse("log(2)");
+decimal resultB = parser.Parse("log(2,3)");
+````
+###Programatically add variables
+```
+/* 
+* when parsing an expression that requires 
+* for instance a variable name declaration 
+* or change, use ProgramaticallyParse().
+*/
+MathParser parser = new MathParser();
+          
+// first way, using let varname = value
+decimal resultA = parser.ProgrammaticallyParse("let a = 2pi");
+Assert.IsTrue (parser.Parse ("a") == (decimal)Math.PI*2);
+
+// second way, using varname :=  value
+decimal resultC = parser.ProgrammaticallyParse("b := 20");
+Assert.IsTrue(parser.Parse("b") == 20);
+
+// third way, using let varname be value
+decimal resultD = parser.ProgrammaticallyParse("let c be 25");
+Assert.IsTrue(resultD == 25);
+```