evaluate_rule.h

#ifndef BASIC_EVALUATE_BASIC_CALC_RULE_H
#define BASIC_EVALUATE_BASIC_CALC_RULE_H

#define N_OPTR 10

#ifndef OPND
#define OPND int
#endif

#define EVALUATE_ERROR Calcresult(INT32_MIN,false)

/*
 * have added <,>and= to the operators.It is not
 * suggested to add these three operators to complex expressions.
 */

const char pri[N_OPTR][N_OPTR] = {
	/*                   |     current   operator     |  */
	/*                   +   -   *   /   (   )  \0   =   <   > */
	/* stack   +     */ '>','>','<','<','<','>','>','>','>','>',
	/* top     -     */ '>','>','<','<','<','>','>','>','>','>',
	/*operator *     */ '>','>','>','>','<','>','>','>','>','>',
	/*         /     */ '>','>','>','>','<','>','>','>','>','>',
	/*         (     */ '<','<','<','<','<','=','?','<','<','<',
	/*         )     */ '?','?','?','?','?','?','?','?','?','?',
	/*         \0    */ '<','<','<','<','<','?','=','<','<','<',
	/*         =     */ '<','<','<','<','<','>','>','>','>','>',
	/*         <     */ '<','<','<','<','<','>','>','>','>','>',
	/*         >     */ '<','<','<','<','<','>','>','>','>','>',
};

typedef enum { ADD, SUB, MUL, DIV, LP, RP, EOE, EQ, LT, GT} Operator;

char orderbetween(char a, char b) {
	int a1, b1;
	switch (a) {
	case '+':a1 = ADD; break;
	case '-':a1 = SUB; break;
	case '*':a1 = MUL; break;
	case '/':a1 = DIV; break;
	case '(':a1 = LP; break;
	case ')':a1 = RP; break;
	case '\0':a1 = EOE; break;
	case '=':a1 = EQ; break;
	case '<':a1 = LT; break;
	case '>':a1 = GT;
	}
	switch (b) {
	case '+':b1 = ADD; break;
	case '-':b1 = SUB; break;
	case '*':b1 = MUL; break;
	case '/':b1 = DIV; break;
	case '(':b1 = LP; break;
	case ')':b1 = RP; break;
	case '\0':b1 = EOE; break;
	case '=':b1=EQ;
	case '<':b1 = LT; break;
	case '>':b1 = GT;
	}
	return pri[a1][b1];
}

#ifndef CALCRESULT
#define CALCRESULT
struct Calcresult{
	bool flag;
	int result;
	Calcresult(int result,bool flag=true):result(result),flag(flag){}
};

#endif
Calcresult calculate(int a, int b, char optr) {
	switch (optr) {
	case '+':return a + b;
	case '-':return a - b;
	case '*':return a * b;
	case '/':return b==0?EVALUATE_ERROR:a/b;
	case '=':return a == b;
	case '>':return a > b;
	case '<':return a < b;
	default:return EVALUATE_ERROR;
	}
}

#endif //BASIC_EVALUATE_BASIC_CALC_RULE_H