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DSBookCode/BookCode/第3章/3.22/3.22.h

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+/***链栈实现表达式求值***/
+
+#include<iostream>
+using namespace std;
+
+const char oper[7] = { '+', '-', '*', '/', '(', ')', '#' };
+#define OK 1
+#define ERROR 0
+#define OVERFLOW -2
+typedef char SElemType;
+typedef int Status;
+typedef struct SNode {
+	int data;
+	struct SNode *next;
+} SNode, *LinkStack;
+
+Status InitStack(LinkStack &S) {
+	S = NULL;
+	return OK;
+}
+bool StackEmpty(LinkStack S) {
+	if (!S)
+		return true;
+	return false;
+}
+Status Push(LinkStack &S, SElemType e) {
+	SNode *p = new SNode;
+	if (!p) {
+		return OVERFLOW;
+	}
+	p->data = e;
+	p->next = S;
+	S = p;
+	return OK;
+}
+Status Pop(LinkStack &S, SElemType &e) {
+	SNode *p;
+	if (!S)
+		return ERROR;
+	e = S->data;
+	p = S;
+	S = S->next;
+	delete p;
+	return OK;
+}
+Status GetTop(LinkStack &S) {
+	if (!S)
+		return ERROR;
+
+	return S->data;
+}
+bool In(char ch) {//判断ch是否为运算符
+	for (int i = 0; i < 7; i++) {
+		if (ch == oper[i]) {
+			return true;
+		}
+	}
+	return false;
+}
+char Precede(char theta1, char theta2) {//判断运算符优先级
+	if ((theta1 == '(' && theta2 == ')') || (theta1 == '#' && theta2 == '#')) {
+		return '=';
+	} else if (theta1 == '(' || theta1 == '#' || theta2 == '(' || (theta1
+			== '+' || theta1 == '-') && (theta2 == '*' || theta2 == '/')) {
+		return '<';
+	} else
+		return '>';
+}
+char Operate(char first, char theta, char second) {//计算两数运算结果
+	switch (theta) {
+	case '+':
+		return (first - '0') + (second - '0') + 48;
+	case '-':
+		return (first - '0') - (second - '0') + 48;
+	case '*':
+		return (first - '0') * (second - '0') + 48;
+	case '/':
+		return (first - '0') / (second - '0') + 48;
+	}
+	return 0;
+}
+
+//算法3.22　表达式求值
+char EvaluateExpression() {//算术表达式求值的算符优先算法，设OPTR和OPND分别为运算符栈和操作数栈
+	LinkStack OPTR, OPND;
+	char ch, theta, a, b, x, top;
+	InitStack(OPND); //初始化OPND栈
+	InitStack(OPTR); //初始化OPTR栈
+	Push(OPTR, '#'); //将表达式起始符“#”压入OPTR栈
+	cin >> ch;
+	while (ch != '#' || (GetTop(OPTR) != '#')) //表达式没有扫描完毕或OPTR的栈顶元素不为“#”
+	{
+		if (!In(ch)) {
+			Push(OPND, ch);
+			cin >> ch;
+		} //ch不是运算符则进OPND栈
+		else
+			switch (Precede(GetTop(OPTR), ch)) //比较OPTR的栈顶元素和ch的优先级
+			{
+			case '<':
+				Push(OPTR, ch);
+				cin >> ch; //当前字符ch压入OPTR栈，读入下一字符ch
+				break;
+			case '>':
+				Pop(OPTR, theta); //弹出OPTR栈顶的运算符
+				Pop(OPND, b);
+				Pop(OPND, a); //弹出OPND栈顶的两个运算数
+				Push(OPND, Operate(a, theta, b)); //将运算结果压入OPND栈
+				break;
+			case '=': //OPTR的栈顶元素是“(”且ch是“)”
+				Pop(OPTR, x);
+				cin >> ch; //弹出OPTR栈顶的“(”，读入下一字符ch
+				break;
+			} //switch
+	} //while
+	return GetTop(OPND); //OPND栈顶元素即为表达式求值结果
+}