参考链接： C 程序，使简单的计算器使用switch ... case进行加，减，乘或除运算
/*
Simple calculator
input from cin,output to cout
简单计算器：支持加减乘除取余、正负数、括号
主要实现：
1.两个类Token和Token_stream：将输入表达式分为单词如1.82， ，（，存储在Token类对象中，Token_stream类实现能缓存1个单词的流
2.三个实现语法的函数expression(),term(),primary()：实现表达式计算顺序
3.计算流程函数calculate():用循环实现任意次数表达式计算，直到出错或正常退出
The grammar is:
Statement:
Expression
Quit
Print:
;
Quit:
q
Expression
Term
Expression Term
Expression - Term
Term:
primary
Term * primary
Term / primary
Term % primary
Primary:
Num
( Expression )
primary
- primary
Num:
floating-point-literal
*/
#include <iostream>
using namespace std;
class Token;
class Token_stream;
void keep_window_open();
double expression();
double term();
double primary();
void welcome();
void calculate();
const char number = '8';
const char print = ';';
const char quit = 'e';
const string prompt = ">";
const string myresult = "=";
class Token{
public:
char m_kind;
double m_value;
Token(char kind = ' ', double value = 0)
:m_kind(kind)
,m_value(value)
{}
};
class Token_stream{
public:
Token get();
void putback(Token t);
Token_stream()
:m_full(false)
,m_buffer(' ', 0)
{}
private:
bool m_full;
Token m_buffer;
};
//定义能够缓存1个单词的流ts
Token_stream ts;
Token Token_stream::get()
{
//缓冲区有单词，从缓冲区中取单词
if(true == m_full){
m_full = false;
return m_buffer;
}
//缓冲区没有单词，从输入流中取单词
char ch;
cin>>ch;
switch(ch){
case ' ':
case '-':
case '*':
case '/':
case '%':
case '(':
case ')':
case print:
case quit:
return Token(ch);
case '.':
case '0':case '1':case '2':case '3':case '4':
case '5':case '6':case '7':case '8':case '9':
{
cin.putback(ch);
double val;
cin>>val;
return Token(number, val);
}
default:
{
cout<<"err input!"<<endl;
keep_window_open();
}
}
}
void Token_stream::putback(Token t)
{
if(true == m_full){
cout<<"err: m_buffer is full."<<endl;
keep_window_open();
return;
}
m_full = true;
m_buffer = t;
}
void keep_window_open()
{
char ch;
fflush(stdin);
cin>>ch;
exit(EXIT_FAILURE);
}
//处理 - 加、减运算
double expression()
{
double left = term();
Token t = ts.get();
while(true){
switch(t.m_kind){
case ' ':
left = term();
t = ts.get();
break;
case '-':
left -= term();
t = ts.get();
break;
default:
ts.putback(t);
return left;
}
}
}
//处理* / % 乘、除、取余运算
double term()
{
double left = primary();
Token t = ts.get();
while(true){
switch(t.m_kind){
case '*':
left *= primary();
t = ts.get();
break;
case '/':
{
double d = primary();
if(0 == d){
cout<<"divide into zero"<<endl;
keep_window_open();
}
left /= d;
t = ts.get();
break;
}
case '%':
{
double d = primary();
int i1 = int(left);
int i2 = int(d);
if(i1 != left){
cout<<"left operand not int"<<endl;
keep_window_open();
}
if(i2 != d){
cout<<"right operand not int"<<endl;
keep_window_open();
}
if(i2 == 0){
cout<<"% divide into 0"<<endl;
}
left = i1 % i2;
t = ts.get();
break;
}
default:
ts.putback(t);
return left;
}
}
}
//处理（）- 括号、正、负运算
double primary()
{
Token t = ts.get();
switch(t.m_kind){
case number:
return t.m_value;
case '(':
double d = expression();
t = ts.get();
if(')' != t.m_kind){
cout<<"expected ')'"<<endl;
keep_window_open();
}
return d;
case '-':
return -primary();
case ' ':
return primary();
default:
cout<<"expected primary!"<<endl;
keep_window_open();
}
}
void calculate()
{
while(cin){
cout<<prompt;
Token t = ts.get();
while(print == t.m_kind)t = ts.get();
if(quit == t.m_kind)return;
else
ts.putback(t);
cout<<myresult<<expression()<<endl;
}
}
void welcome()
{
cout<<"Welcome to our simple calculator."<<endl
<<"-----------------------------"<<endl
<<"floating-point numbers"<<endl
<<"operator: ' ' '-' '*' '/' '%'"<<endl
<<"negative: '-'"<<endl
<<"positive: ' '"<<endl
<<"end of expression: ';'"<<endl
<<"quit: 'e'"<<endl
<<"-----------------------------"<<endl;
}
int main()
{
welcome();
calculate();
cout<<"See you."<<endl;
keep_window_open();
return 0;
}
