PLC Laboratory 6
Contents
Interpreter of Arithmetic Expressions Using Recursive Descent Parser
Using recursive descent, implement an interpreter of arithmetic expressions. These expressions contain +, -, *, / operators (with common priorities and left associativity) and parentheses. To simplify the task, consider we have only binary operators. There are no unary operators in our language. Moreover, we can use only positive integers in our expressions.
For the recursive descent use following grammar:
E : T E1; (1)
E1 : '+' T E1 (2)
| '-' T E1 (3)
| {e}; (4)
T : F T1; (5)
T1 : '*' F T1 (6)
| '/' F T1 (7)
| {e} (8)
F : '(' E ')' (9)
| num (10)
To simplify the solution you can use the lexical analyzer from Laboratory 2
You can use this Parser in C#
Input specification
The first line of the input contains a number N. It defines the number of expressions your program should evaluate. These expressions are on next N lines. Each line contains exactly one expression.
Output specification
For each expression write one line containing the result – the computed value of the expression. If there is any error in the input, write text ERROR instead.
Example
- Input
2
2 * (3+5)
15 - 2**7
- Output
16
ERROR
