APPLYING C++ in .NET

Encode QR Code ISO/IEC18004 in .NET APPLYING C++

APPLYING C++
QR Code JIS X 0510 Maker In VS .NET
Using Barcode encoder for Visual Studio .NET Control to generate, create QR Code 2d barcode image in .NET framework applications.
QR Decoder In VS .NET
Using Barcode recognizer for .NET Control to read, scan read, scan image in VS .NET applications.
C++: The Complete Reference
Making Barcode In .NET Framework
Using Barcode generator for .NET framework Control to generate, create barcode image in VS .NET applications.
Barcode Decoder In .NET
Using Barcode decoder for .NET Control to read, scan read, scan image in VS .NET applications.
The Parser Class
QR Code Creator In Visual C#.NET
Using Barcode creator for .NET Control to generate, create Denso QR Bar Code image in .NET framework applications.
QR Creation In Visual Studio .NET
Using Barcode generator for ASP.NET Control to generate, create QR Code image in ASP.NET applications.
The expression parser is built upon the parser class The first version of parser is shown here Subsequent versions of the parser build upon it
QR-Code Creation In VB.NET
Using Barcode creation for .NET Control to generate, create QR Code JIS X 0510 image in .NET framework applications.
Paint Code-39 In .NET Framework
Using Barcode encoder for Visual Studio .NET Control to generate, create USS Code 39 image in .NET applications.
class parser { char *exp_ptr; // points to the expression char token[80]; // holds current token char tok_type; // holds token's type void eval_exp2(double &result); void eval_exp3(double &result); void eval_exp4(double &result); void eval_exp5(double &result); void eval_exp6(double &result); void atom(double &result); void get_token(); void serror(int error); int isdelim(char c); public: parser(); double eval_exp(char *exp); };
USS Code 128 Generation In VS .NET
Using Barcode creation for .NET framework Control to generate, create Code 128B image in Visual Studio .NET applications.
Generating Bar Code In VS .NET
Using Barcode generation for VS .NET Control to generate, create barcode image in .NET applications.
The parser class contains three private member variables The expression to be evaluated is contained in a null-terminated string pointed to by exp_ptr Thus, the parser evaluates expressions that are contained in standard ASCII strings For example, the following strings contain expressions that the parser can evaluate: "10 5" "2 * 33 / (31416 * 33)" When the parser begins execution, exp_ptr must point to the first character in the expression string As the parser executes, it works its way through the string until the null-terminator is encountered The meaning of the other two member variables, token and tok_type, are described in the next section The entry point to the parser is through eval_exp( ), which must be called with a pointer to the expression to be analyzed The functions eval_exp2( ) through eval_exp6( ) along with atom( ) form the recursive-descent parser They implement an enhanced set of the expression production rules discussed earlier In subsequent versions of the parser, a function called eval_exp1( ) will also be added
Generating DataMatrix In VS .NET
Using Barcode encoder for .NET Control to generate, create Data Matrix ECC200 image in .NET framework applications.
Code11 Generator In Visual Studio .NET
Using Barcode printer for Visual Studio .NET Control to generate, create USD8 image in VS .NET applications.
40:
Painting UPC-A Supplement 5 In None
Using Barcode creator for Microsoft Word Control to generate, create Universal Product Code version A image in Word applications.
Code 39 Extended Creation In None
Using Barcode printer for Font Control to generate, create Code-39 image in Font applications.
Parsing Expressions
Encoding Code 39 In Java
Using Barcode generator for Java Control to generate, create ANSI/AIM Code 39 image in Java applications.
Creating GS1 DataBar-14 In Java
Using Barcode generator for Java Control to generate, create DataBar image in Java applications.
The serror( ) handles syntax errors in the expression The functions get_token( ) and isdelim( ) are used to dissect the expression into its component parts, as described in the next section
Painting DataMatrix In Java
Using Barcode printer for Java Control to generate, create Data Matrix ECC200 image in Java applications.
Barcode Scanner In Java
Using Barcode recognizer for Java Control to read, scan read, scan image in Java applications.
Dissecting an Expression
UCC-128 Generation In Objective-C
Using Barcode creator for iPhone Control to generate, create UCC-128 image in iPhone applications.
Bar Code Generation In Visual C#
Using Barcode maker for Visual Studio .NET Control to generate, create bar code image in .NET applications.
In order to evaluate expressions, you need to be able to break an expression into its components Since this operation is fundamental to parsing, let's look at it before examining the parser itself Each component of an expression is called a token For example, the expression A * B (W + 10) contains the tokens A, *, B, , (, W, +, 10, and ) Each token represents an indivisible unit of the expression In general, you need a function that sequentially returns each token in the expression individually The function must also be able to skip over spaces and tabs and detect the end of the expression The function that we will use to perform this task is called get_token( ), which is a member function of the parser class Besides the token, itself, you will also need to know what type of token is being returned For the parser developed in this chapter, you need only three types: VARIABLE, NUMBER, and DELIMITER (DELIMITER is used for both operators and parentheses) The get_token( ) function is shown here It obtains the next token from the expression pointed to by exp_ptr and puts it into the member variable token It puts the type of the token into the member variable tok_type
// Obtains the next token void parser::get_token() { register char *temp; tok_type = 0; temp = token; *temp = '\0'; if(!*exp_ptr) return; // at end of expression while(isspace(*exp_ptr)) ++exp_ptr; // skip over white space if(strchr("+-*/%^=()", *exp_ptr)){ tok_type = DELIMITER; APPLYING C++
C++: The Complete Reference
// advance to next char *temp++ = *exp_ptr++; } else if(isalpha(*exp_ptr)) { while(!isdelim(*exp_ptr)) *temp++ = *exp_ptr++; tok_type = VARIABLE; } else if(isdigit(*exp_ptr)) { while(!isdelim(*exp_ptr)) *temp++ = *exp_ptr++; tok_type = NUMBER; } *temp = '\0'; } // Return true if c is a delimiter int parser::isdelim(char c) { if(strchr(" +-/*%^=()", c) || c==9 || c=='\r' || c==0) return 1; return 0; }
Look closely at the preceding functions After the first few initializations, get_token( ) checks to see if the null terminating the expression has been found It does so by checking the character pointed to by exp_ptr Since exp_ptr is a pointer to the expression being analyzed, if it points to a null, the end of the expression has been reached If there are still more tokens to retrieve from the expression, get_token( ) first skips over any leading spaces Once the spaces have been skipped, exp_ptr is pointing to either a number, a variable, an operator, or if trailing spaces end the expression, a null If the next character is an operator, it is returned as a string in token, and DELIMITER is placed in tok_type If the next character is a letter instead, it is assumed to be one of the variables It is returned as a string in token, and tok_type is assigned the value VARIABLE If the next character is a digit, the entire number is read and placed in its string form in token and its type is NUMBER Finally, if the next character is none of the preceding, it is assumed that the end of the expression has been reached In this case, token is null, which signals the end of the expression As stated earlier, to keep the code in this function clean, a certain amount of error checking has been omitted and some assumptions have been made For example, any unrecognized character may end an expression Also, in this version, variables may be of any length, but only the first letter is significant You can add more error checking and other details as your specific application dictates
40:
Copyright © OnBarcode.com . All rights reserved.