Expression evaluation is a common need in many programs, especially if you deal with numbers and operators.
|(Declarations)||Declarations||Declarations and private variables for the CExpressionEvaluator class.|
|Expression||Property||Get the expression to evaluate.|
|Postfix||Property||Get the postfix representation of the expression string.|
|Class_Initialize||Initialize||Set initial values to defaults which may be overridden with property settings.|
|Evaluate||Method||Evaluates the expression. For simplicity the postfix representation of the expression is evaluated.|
|CharType||Private||Determine the type of the current character.|
|ConvertToPostfix||Private||Converts the expression to postfix and stores the result in m_strPostfix.|
|GetNextToken||Private||Get the next token in the string identified by the text property.|
|HandleSeparator||Private||Handles a separator character.|
|HandleToken||Private||Handles a token character.|
|HandleWhiteSpace||Private||Handles a whitespace character.|
|ParseExpression||Private||Parses an expression.|
|ParseFactor||Private||Parses a factor.|
|ParseTerm||Private||Parse a term. A term is something like 2+7, or 1 + sin(1), while a token is the smallest meaningful piece of data, such as 2 or sin.|
|PopResult||Private||Pops an item off the stack.|
|PushResult||Private||Pushes an item onto the stack.|
|SetTokenString||Private||Set the string used by the tokenizer.|
' Example of CExpressionEvaluator ' ' To try this example, do the following: ' 1. Add a command button named 'cmdTest' ' 2. Paste all the code from this example to the new form's module. ' 3. Run the form Private mExpressionEvaluator As CExpressionEvaluator Private Sub cmdTest_Click() Dim dblResult As Double Set mExpressionEvaluator = New CExpressionEvaluator With mExpressionEvaluator .Expression = "5 * 10 / (12.5 * 2)" dblResult = .Evaluate Debug.Print "5 * 10 / (12.5 * 2) = " & dblResult End With End Sub
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