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visual basic barcode program 2: A RecursiveDescent Expression Parser in Java
2: A RecursiveDescent Expression Parser PDF 417 Scanner In Java Using Barcode Control SDK for Java Control to generate, create, read, scan barcode image in Java applications. Drawing PDF417 In Java Using Barcode encoder for Java Control to generate, create PDF 417 image in Java applications. Assume this precedence for each operator: Highest
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Barcode Scanner In Java Using Barcode reader for Java Control to read, scan read, scan image in Java applications. Draw PDF 417 In Visual C# Using Barcode generation for VS .NET Control to generate, create PDF417 2d barcode image in .NET applications. Lowest
PDF417 2d Barcode Drawer In .NET Framework Using Barcode encoder for ASP.NET Control to generate, create PDF 417 image in ASP.NET applications. Paint PDF417 In .NET Using Barcode drawer for Visual Studio .NET Control to generate, create PDF 417 image in .NET framework applications. Operators of equal precedence evaluate from left to right. The parser developed here will be subject to a few constraints. First, all variables are single letters (in other words, 26 variables, A through Z, are available). The variables are not case sensitive (a and A are treated as the same variable). Second, all numeric values are assumed to be double, although you could easily modify the parser to handle other types of values. Finally, to keep the logic clear and easy to understand, only rudimentary error checking is included. Creating PDF417 In VB.NET Using Barcode creation for .NET Control to generate, create PDF417 image in VS .NET applications. Code128 Maker In Java Using Barcode generator for Java Control to generate, create Code 128 image in Java applications. Parsing Expressions: The Problem
Barcode Generator In Java Using Barcode creation for Java Control to generate, create barcode image in Java applications. 1D Barcode Generation In Java Using Barcode encoder for Java Control to generate, create Linear image in Java applications. If you have not thought much about the problem of expression parsing, you might assume that it is a simple task, but it isn't. To better understand the problem, try to evaluate this sample expression: 10 2 * 3 You know that this expression is equal to the value 4. Although you could easily create a program that would compute that specific expression, the problem is how to create a program that gives the correct answer for any arbitrary expression. At first you might think of an algorithm something like this: a = get first operand while(operands present) { op = get operator b = get second operand a = a op b } This approach gets the first operand, the operator, and the second operand to perform the first operation, and then gets the next operator and operand to perform the next operation, and so on. However, if you try this basic approach, the expression 10 2 * 3 evaluates to 24 (that is, 8 * 3) instead of 4 because this procedure neglects the precedence of the operators. You cannot just take the operands and operators in order from left to right because the rules of algebra dictate that multiplication must be done before subtraction. Some beginners think that this problem can be easily overcome, and sometimes, in very restricted cases, it can. But the problem only gets worse when you add parentheses, exponentiation, variables, unary operators, and the like. Printing USD4 In Java Using Barcode creator for Java Control to generate, create ABC Codabar image in Java applications. Read Code128 In .NET Framework Using Barcode reader for VS .NET Control to read, scan read, scan image in .NET applications. The Art of Java
Read GTIN  128 In Visual C# Using Barcode reader for VS .NET Control to read, scan read, scan image in Visual Studio .NET applications. ECC200 Creator In .NET Using Barcode maker for Reporting Service Control to generate, create DataMatrix image in Reporting Service applications. Although there are a number of ways to write the code that processes an expression, the one developed here is the approach most easily written by a person. It is called a recursivedescent parser, and in the course of this chapter you will see how it got its name. (Some of the other methods used to write parsers employ complex tables that are usually generated by another computer program. These are sometimes called tabledriven parsers.) Drawing Matrix 2D Barcode In .NET Framework Using Barcode creation for Visual Studio .NET Control to generate, create Matrix 2D Barcode image in .NET applications. Printing EAN 128 In None Using Barcode creation for Font Control to generate, create GS1128 image in Font applications. Parsing an Expression
Make 1D In VB.NET Using Barcode creator for Visual Studio .NET Control to generate, create Linear Barcode image in VS .NET applications. Barcode Drawer In None Using Barcode generator for Font Control to generate, create bar code image in Font applications. There are a number of ways to parse and evaluate an expression. For use with a recursivedescent parser, think of expressions as recursive data structures that is, expressions that are defined in terms of themselves. If, for the moment, we assume that expressions can only use +, , *, /, and parentheses, all expressions can be defined with the following rules: expression term [+ term] [ term] term factor [* factor] [/ factor] factor variable, number, or (expression) The square brackets designate an optional element, and the means produces. In fact, the rules are usually called the production rules of the expression. Therefore, for the definition of term you could say: Term produces factor times factor or factor divided by factor. Notice that the precedence of the operators is implicit in the way an expression is defined. Here is an example. The expression 10 + 5 * B has two terms: 10 and 5 * B. The second term contains two factors: 5 and B. These factors consist of one number and one variable. On the other hand, the expression 14 * (7 C) has two factors: 14 and (7 C). The factors consist of one number and one parenthesized expression. The parenthesized expression contains two terms: one number and one variable. This process forms the basis for a recursivedescent parser, which is a set of mutually recursive methods that work in a chainlike fashion and implement the production rules. At each appropriate step, the parser performs the specified operations in the algebraically correct sequence. To see how the production rules are used to parse an expression, let s work through an example using the following expression: 9/3 (100 + 56) Here is the sequence that you will follow:

