The following example shows the contents of the calc.yacc file.

When you use the variable in subsequent calculations, it will have the assigned value: When you press the Enter key, the program displays the result of the operation. Then enter numbers and operators in calculator fashion. In either case, after you start the program, the cursor moves to the line below the $ (command prompt). Or, to move the program to a file with a more descriptive name, as in the following example, and run it, enter: To then run the program directly from the a.out file, enter: The object file for the lex.yy.c source file The object file for the y.tab.c source file

Compile and link the two C language source files:.

The C language source file that the lex command created for the lexical analyzer.

Use the li command to verify that the following file was created:.

The C language source file that the yacc command created for the parser.Ī header file containing define statements for the tokens used by the parser.

Use the li command to verify that the following files were created:.

Process the yacc grammar file using the -d optional flag (which tells the yacc command to create a file that defines the tokens used in addition to the C language source code):.

Perform the following steps, in order, to create the desk calculator example program: The following descriptions assume that the calc.lex and calc.yacc example programs are found in your current directory. Specifies the yacc command grammar file that defines the parsing rules, and calls the yylex subroutine created by the lex command to provide input. Specifies the lex command specification file that defines the lexical analysis rules. The files that contain the example lex and yacc programs are: File This calculator program also allows you to assign values to variables (each designated by a single, lowercase letter) and then use the variables in calculations.

Together, these example programs create a simple, desk-calculator program that performs addition, subtraction, multiplication, and division operations. This section describes example programs for the lex and yacc commands. Example Program for the lex and yacc ProgramsĪIX Version 4.3 General Programming Concepts: Writing and Debugging Programs

Lex compiler online