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cbisonflex-lexeryacc

Variables Calculator Bison and flex

How can i Write a LEX and Bison Program to recognize a valid arithmetic expression that uses operators +, -, * and /and It gives priority to parentheses () and Accepts definition of variables and this variables can include the previous expressions and operations?

m=5
y=9+5
Solution

  • This question is a bit open-ended to fully answer. In brief, you will need Bison rules for an expression that looks something like:

    varassign : VARIABLE '=' exp
    ;

exp : '(' exp ')'
    | exp '+' exp
    | exp '-' exp
    | '-' exp
    | NUMBER
    ;

    You will need to specify the precedence of operators. Refer to the Bison Manual section Specifying Operator Precedence for details.

    For lex, you just need to return the single-character tokens, and have a rule that parses [0-9]+ as a NUMBER token. And presumably you return any non-keyword string of letters as VARIABLE.