I believe the precedence of arithmetic operations must have greater value than one

Part 07 precedence of comparisons about acwj HOT 3 OPEN

doctorwkt commented on August 20, 2024 3

Part 07 precedence of comparisons

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Comments (3)

jamestjw commented on August 20, 2024

I agree with your take on this, below is a snippet of operator precedence from the SubC compiler

static int Prec[] = {
	7, /* SLASH */
	7, /* STAR */
	7, /* MOD */
	6, /* PLUS */
	6, /* MINUS */
	5, /* LSHIFT */
	5, /* RSHIFT */
	4, /* GREATER */
	4, /* GTEQ */
	4, /* LESS */
	4, /* LTEQ */
	3, /* EQUAL */
	3, /* NOTEQ */
	2, /* AMPER */
	1, /* CARET */
	0, /* PIPE */
};

and indeed we can see that the comparison operators have lesser precedence than the arithmetic operators, and the equality operators have lesser precedence than the comparison operators

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mxysfive commented on August 20, 2024

I also meet this problem. When I input 2 + 7 < 9 the author's code return 3 rather than 0.

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vcheckzen commented on August 20, 2024

Yes, the author could have done the wrong thing. The precedence order is not consistent with this doc which is even mentioned by the author in Readme. In this chapter, the precedence table should be adjusted to the following.

// Operator precedence for each token. Must
// match up with the order of tokens in defs.h
// Larger ones should first be caculated.
static int OpPrec[] = {
   0,                           // T_EOF
  30, 30,                       // T_PLUS, T_MINUS
  40, 40,                       // T_STAR, T_SLASH
  10, 10,                       // T_EQ, T_NE
  20, 20, 20, 20                // T_LT, T_GT, T_LE, T_GE
};