Data_Structure/Chapter3/ValExpression/Expresion.cpp

#include<iostream>		//cout,cin
using namespace std;
#include"SqStack.h"

char pause;

char Precede(char t1, char t2)								//算符的优先级比较
{
	char f;
	switch (t2)
	{
	case '+':
	case '-':if (t1 == '(' || t1 == '=')
		f = '<';
			else
		f = '>';
		break;
	case '*':
	case '/':if (t1 == '*' || t1 == '/' || t1 == ')')
		f = '>';
			else
		f = '<';
		break;
	case '(':if (t1 == ')')
	{
		cout << "ERROR1" << endl;
		exit(0);
	}
			else
		f = '<';
		break;
	case ')':switch (t1)
	{
	case '(':f = '=';
		break;
	case '=':cout << "ERROR2" << endl;
		exit(0);
	default: f = '>';
	}
			break;
	case '=':switch (t1)
	{
	case '=':f = '=';
		break;
	case '(':cout << "ERROR2" << endl;
		exit(0);
	default: f = '>';
	}
	}
	return f;
}


bool In(char ch)										// 判断 ch 是否为运算符
{
	switch (ch)
	{
	case'+':
	case'-':
	case'*':
	case'/':
	case'(':
	case')':
	case'=':return true;
	default:return false;
	}
}


float Operate(float a, char theta, float b)
{													// 实施一次运算
	float ch;
	switch (theta)
	{
	case'+':ch = a + b;
		break;
	case'-':ch = a - b;
		break;
	case'*':ch = a * b;
		break;
	case'/':ch = a / b;
	}
	return ch;
}

//算法3.12 
float Val_Exp(char* exp)								// 中缀表达式求值。
{
	SqStack<char>   OP;									// 运算符栈
	SqStack<float>  OD;									// 运算数栈
	InitStack(OP, 30);
	InitStack(OD, 30);
	char theta;
	float a, b, result;
	char ch, x;											// 存放由键盘接收的字符
	char z[6];											// 存放符点数字符串
	int i;
	Push(OP, '=');										// # 是表达式结束标志
	ch = *exp++;
	GetTop(OP, x);
	while (ch != '=' || x != '=')
	{
		if (ch >= '0' && ch <= '9' || ch == '.')					// ch 是操作数
		{
			i = 0;
			do
			{
				z[i] = ch;
				i++;
				ch = *exp++;
			} while (ch >= '0' && ch <= '9' || ch == '.');
			z[i] = '\0';
			result = atof(z);										// 将字符串数组转为符点型存于result
			Push(OD, result);
		}
		else if (In(ch))											// 是7种运算符之一
			switch (Precede(x, ch))
			{
			case'<':Push(OP, ch);							// 栈顶元素优先权低
				ch = *exp++;
				break;
			case'=':Pop(OP, x);								// 脱括号并接收下一字符
				ch = *exp++;
				break;
			case'>':Pop(OP, theta);							// 退栈并将运算结果入栈
				Pop(OD, b);
				Pop(OD, a);
				Push(OD, Operate(a, theta, b));
			}
		else												// ch是非法字符
		{
			cout << "ERROR3" << endl;;
			exit(0);
		}
		GetTop(OP, x);
	}
	GetTop(OD, result);
	DestroyStack(OP);
	DestroyStack(OD);
	return result;
}

void CreatePostExp(char* exp, char*& postexp)			// 由中缀式求后缀式
{
	char ch, x;
	int i = 0;
	SqStack<char> OP;
	InitStack(OP, 30);
	Push(OP, '=');										// # 是表达式结束标志
	cout << "中缀表达式：" << exp << endl;
	ch = *exp++;
	while (ch)
	{
		if ((ch >= '0' && ch <= '9') || ch == '.')
		{
			postexp[i++] = ch;
			ch = *exp++;
		}
		if (In(ch))										// 是7种运算符之一
		{
			postexp[i++] = ' ';
			GetTop(OP, x);
			switch (Precede(x, ch))
			{
			case'<':Push(OP, ch);						// 栈顶元素优先权低
				ch = *exp++;
				break;
			case'=':Pop(OP, x);						// 脱括号并接收下一字符
				ch = *exp++;
				break;
			case'>':
				Pop(OP, postexp[i++]);				// 运算符出栈输出
				break;
			}
		}
		postexp[i] = '\0';
	}//while
	cout << "\n后缀表达式为:" << postexp << endl;
	DestroyStack(OP);
}

//算法3.13  
float Val_PostExp(char* postexp)						// 后缀表达式求值
{
	int i;
	char z[6];
	float result = 0, d = 0, a, b;
	char ch;
	SqStack<float> OD;
	InitStack(OD, 30);
	ch = *postexp++;
	while (ch != '\0')
	{

		if (ch >= '0' && ch <= '9' || ch == '.')						// ch为操作数符号
		{
			i = 0;
			do
			{
				z[i++] = ch;
				ch = *postexp++;							// 取下一个操作数符号
			} while (ch >= '0' && ch <= '9' || ch == '.');
			z[i] = '\0';
			d = atof(z);									// 将字符串数组转为符点型存于result
			Push(OD, d);									// 操作数进栈
		}
		if (In(ch))										// ch为运算符
		{
			Pop(OD, a);
			Pop(OD, b);
			Push(OD, Operate(b, ch, a));
			ch = *postexp++;
		}
		ch = *postexp++;
	}
	Pop(OD, result);
	DestroyStack(OD);
	return result;
}


//主函数
void main()
{
	//int i;
	char exp[20] = "(2.2+5)+4*(5-3.1)=";
	char* postexp;
	postexp = new char[30];
	*postexp = '\0';
	float v;
	system("cls");										// 清屏
	cout << "\n缺省表达式：" << exp;
	cout << endl;
	int choice;
	do
	{													// 显示主菜单
		cout << endl;
		cout << "1-创建表达式\n";
		cout << "2-表达式求值\n";
		cout << "3-求后缀表达式\n";
		cout << "4-后缀表达式求值\n";
		cout << "5-显示表达式\n";
		cout << "0-退出\n";
		cout << "输入功能选项（1~5，0 退出）:\n";
		cin >> choice;
		switch (choice)
		{
		case 1:										// 创建表达式
			cout << "\n请输入表达式，以=结束" << endl;
			cin >> exp;
			break;
		case 2:										// 表达式求值
			v = Val_Exp(exp);
			cout << exp;
			cout << v << endl;
			break;
		case 3:										// 求后缀表达式
			CreatePostExp(exp, postexp);
			break;
		case 4:										// 后缀表达式求值
			v = Val_PostExp(postexp);
			cout << '\n' << postexp << "=" << v << endl;
			break;
		case 5:										// 显示表达式
			cout << endl;
			cout << "\n已创建的表达式为：";
			cout << exp << endl;
			if (strlen(postexp))
			{
				cout << "\n后缀表达式为：";
				cout << postexp << endl;
			}
			break;
		case 0:										// 退出
			cout << "\n结束运行，Bye-Bye!" << endl;
			break;
		default://
			cout << "\n无效选择!\n";
			break;
		}
	} while (choice != 0);
}//end main