doongjohn / rustcalc

simple calculator

simple calculator

rustcalc) 1+1+1
= 3
rustcalc) 1+1*3
= 4
rustcalc) 3*(2+3)
= 15
rustcalc) 3+2*2^3
= 19
rustcalc) (1+1
Error: expected one of {InfixOperator, ParenthesisClose} but found EOF at index 4

features

• no heap allocation except
  • reading an input
  • generating the error message
• all numbers are f64
• predefined constatns
  • ['pi', 'tau', 'e']
• unary opeartor
  • ['+', '-']
• infix operator
  • ['+', '-', '*', '/', '^']
  • operator precedence
• nested parentheses
• simple error message

todo

• support builtin function (sqrt, abs, floor, ceil, round, ...)
• support imaginary number
• support custom variable (declaration, assignment)
• support custom function (infix, unary)

operator precedence algorithm

• if char is number:
  • state.num = number
• if char is operator:
  • if state.op_prec == current op_prec:

    let op_fn = get_op_fn(state.op_list[prec].op);
    state.num = op_fn(state.op_list[prec].num, state.num);
    state.op_list[prec] = None;

  • if state.op_prec > current op_prec:

    for p in (0..=state.op_list.high).rev() {
        let op_fn = get_op_fn(state.op_list[p].op);
        state.num = op_fn(state.op_list[p].num, state.num);
        state.op_list[p] = None;
    }

    • update state
      • store current op_prec to state.op_prec
      • store state.num to state.op_list[prec].num
      • store operator to state.op_list[prec].op