update computation of infix expression, tests passed.

thu_dsa/chp4/stackApp.cpp

@@ -1,11 +1,20 @@
 #include "../chp2/Fib.h"
 #include "stackApp.h"
+#include <string>
+
+/*-----------build-in functions----------*/
+int readNumber(char* &expr);
+int fac(int n);
+inline char orderBetween(char optr1, char optr2);
+int findOptr(char optr);
+double cal(char optr, double opnd);
+double cal(double opnd1, char optr, double opnd2);
 
 /*
-* @brief : convert a decimal digit n to any base(2 <= base <= 36)
+ * @brief : convert a decimal digit n to any base(2 <= base <= 36)
-* @args  :
+ * @args  :
-* @return: return the result in the form of char*
+ * @return: return the result in the form of char*
-*/
+ */
 char* convert(__int64 n, int base){
 	Stack<char> charStack;
 	while(n != 0){
@@ -20,13 +29,13 @@ char* convert(__int64 n, int base){
 }
 
 /*
-* @brief : to judge if an expression of matches
+ * @brief : to judge if an expression of matches
-* @args  : exp
+ * @args  : exp
-* @return: return true if matches
+ * @return: return true if matches
-*/
+ */
 bool paren(const char exp[]){
 	Stack<char> parenStack;
-	char currParen, popped;
+	char currParen;
 	for(int ix = 0; (currParen = exp[ix]) != '\0'; ++ix){
 		switch(currParen){
 		case '(':
@@ -53,3 +62,119 @@ bool paren(const char exp[]){
 	}
 	return parenStack.empty()? true : false;
 }
+
+/*
+ * @brief : to compute the value of an infix expression
+ * @args  : infixExpr
+ * @return: return the value in double
+ * @others: only consider valid infix expression
+ */
+double evaluate(char* infixExpr){
+	Stack<double> opnd;
+	Stack<char>   optr;
+	double opnd1, opnd2;
+	optr.push('\0');
+	while(!optr.empty()){
+		if (isdigit(*infixExpr)) opnd.push(readNumber(infixExpr));
+		else{
+			if (*infixExpr == ' ' || *infixExpr == '\t') { // skip white spaces
+				++infixExpr;
+				continue;
+			}
+
+			switch(orderBetween(optr.top(), *infixExpr)){
+			case '>':
+				if (optr.top() == '!') opnd.push(cal(optr.pop(), opnd.pop()));
+				else{
+					opnd2 = opnd.pop();
+					opnd1 = opnd.pop();
+					opnd.push(cal(opnd1, optr.pop(), opnd2));
+				}
+				break;
+
+			case '<':
+				optr.push(*infixExpr++);
+				break;
+
+			case '=':
+				infixExpr++;
+				optr.pop();
+				break;
+			}
+		}
+	}
+	return opnd.pop();
+}
+
+/*-----------build-in functions----------*/
+int readNumber(char* &expr){
+	int res = 0;
+	while(isdigit(*expr)){
+		res = res * 10 + *expr - '0';
+		expr++;
+	}
+	return res;
+}
+
+inline char orderBetween(char optr1, char optr2){
+	return pri[findOptr(optr1)][findOptr(optr2)];
+}
+
+int findOptr(char optr){
+	if (optr == '+')  return 0;
+	if (optr == '-')  return 1;
+	if (optr == '*')  return 2;
+	if (optr == '/')  return 3;
+	if (optr == '^')  return 4;
+	if (optr == '!')  return 5;
+	if (optr == '(')  return 6;
+	if (optr == ')')  return 7;
+	if (optr == '\0') return 8;
+}
+
+int fac(int n){
+	int res = 1;
+	for (; n != 0; res *= n, n--);
+	return res;
+}
+
+double cal(char optr, double opnd){
+	double res = 0.0;
+	switch(optr){
+	case '!':
+		res = fac(opnd);
+		break;
+	default:
+		break;
+	}
+	return res;
+}
+
+double cal(double opnd1, char optr, double opnd2) {
+	double res = 0.0;
+	switch (optr){
+	case '+':
+		res = opnd1 + opnd2;
+		break;
+
+	case '-':
+		res = opnd1 - opnd2;
+		break;
+
+	case '*':
+		res = opnd1 * opnd2;
+		break;
+
+	case '/':
+		res = opnd1 / opnd2;
+		break;
+
+	case '^':
+		res = pow(opnd1, opnd2);
+		break;
+
+	default:
+		break;
+	}
+	return res;
+}

thu_dsa/chp4/stackApp.h

@@ -3,6 +3,8 @@
 
 #include "Stack.h"
 
+#define NOPTR 9
+
 static char digits[] = { '0','1','2','3','4','5','6','7','8','9',
 						'a','b','c','d','e','f','g','h','i','j',
 						'k','l','m','n','o','p','q','r','s','t',
@@ -15,10 +17,31 @@ static char digits[] = { '0','1','2','3','4','5','6','7','8','9',
 char* convert(__int64 n, int base);
 
 /*
-* @brief : to judge if an expression of parens matches
+ * @brief : to judge if an expression of parens matches
-* @args  : exp
+ * @args  : exp
-* @return: return true if matches
+ * @return: return true if matches
-*/
+ */
 bool paren(const char exp[]);
 
+//pri[stack top optr][curr optr]
+const char pri[NOPTR][NOPTR] = {
+	/*          +    -    *    /    ^    !    (    )    \0 */
+	/*  +  */  '>', '>', '<', '<', '<', '<', '<', '>', '>',
+	/*  -  */  '>', '>', '<', '<', '<', '<', '<', '>', '>',
+	/*  *  */  '>', '>', '>', '>', '<', '<', '<', '>', '>',
+	/*  /  */  '>', '>', '>', '>', '<', '<', '<', '>', '>',
+	/*  ^  */  '>', '>', '>', '>', '>', '<', '<', '>', '>',
+	/*  !  */  '>', '>', '>', '>', '>', '>', '<', '>', '>',
+	/*  (  */  '<', '<', '<', '<', '<', '<', '<', '=', ' ',
+	/*  )  */  ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ',
+	/*  \0 */  '<' ,'<', '<', '<', '<', '<', '<', ' ', '=' };
+
+/*
+ * @brief : to compute the value of an infix expression
+ * @args  : infixExpr
+ * @return: return the value in double
+ * @others: only consider valid infix expression 
+ */
+double evaluate(char* infixExpr);
+
 #endif

thu_dsa/chp4/testStackApp.cpp

@@ -8,11 +8,13 @@ using std::endl;
 
 void test_convert();
 void test_paren();
+void test_evaluate();
 
 int main(){
 	cout << "Running tests......" << endl;
 	test_convert();
 	test_paren();
+	test_evaluate();
 	
 	cout << "All tests passed." << endl;
 	system("pause");
@@ -31,3 +33,8 @@ void test_paren(){
 	assert(paren("[(])") == false);
 	assert(paren("{[()]{[({})]}}") == true);
 }
+
+void test_evaluate(){
+	assert(evaluate("2*5+(3+4-2*7)/2") == 6.5);
+	assert(evaluate("(0!+ 1) * 2 ^ (3!+ 4) - (5!- 67 - (8 + 9))") == 2012);
+}