基本分析可以看另一篇文章C++实现四则运算器(无括号)
栈的实现
//stack.h
#ifndef STACK_H
#define STACK_H
#include<iostream>
class stack_int
{
private:
int* bottom; //栈底
int* top; //栈顶
unsigned int capacity;//栈容量
unsigned int size; //栈大小
public:
stack_int() :bottom(new int[11]), top(bottom), capacity(10), size(0) {};
stack_int(unsigned int capacity) :bottom(new int[capacity+1]),top(bottom), capacity(capacity),size(0){};
int operator[](unsigned int i) const
{
return *(bottom + i);
}
bool isEmpty()const { return bottom == top; }
bool isFull()const { return size == capacity-1; }
unsigned int getsize()const { return size; }
unsigned int getcapacity()const { return capacity; }
int gettop()const
{
if (!isEmpty())
return *(top - 1);
else
return -1;
}
void settop(int i)
{
if (!isEmpty())
{
*(top - 1) = i;
}
}
void push(int i)
{
if ((top - bottom)<capacity)
{
*top = i;
top++;
size++;
}
else
{
std::cout << "stack full!" << std::endl;
stack_expansion();
push(i);
}
}
int pop(int &val)
{//返回值为1则栈未空，返回值为0则栈已空无法出栈
if (top > bottom)
{
top--;
size--;
val = *top;
return 1;
}
else
{
std::cout << "stack empty!" << std::endl;
return NULL;
}
}
private:
void stack_expansion()
{//栈扩容
std::cout << "正在扩容中..." << std::endl;
int newcapacity = 2 * capacity + 1;
int* newbottom = new int[newcapacity + 1];
int* newtop = newbottom;
for (int i = 0; i < size; ++i)
{
*newtop = *bottom;
newtop++;
bottom++;
}
bottom = newbottom;
top = newtop;
capacity = newcapacity;
}
};
#endif
主程序
//Main.c
#include"stack.h"
#include<iostream>
using namespace std;
bool is_digit(char i)
{//是数字
if (i == '1' || i == '2' || i == '3' || i == '4' || i == '5' || i == '6' || i == '7' || i == '8' || i == '9' || i == '0')
return true;
else return false;
}
bool is_operator(char i)
{//是运算符
if (i == '+' || i == '-' || i == '*' || i == '/' || i == '(' || i == ')'||i=='=')
return true;
else return false;
}
bool get_priority(char pre,char cur)
{//获取两个符号间的优先级,pre为靠前的字符，cur为靠后的字符
if ((pre == '+' || pre == '-') && (cur == '*' || cur == '/'))
return false;
else if (pre == '(' || cur == '(')
return false;
else
return true;
}
int do_operation(int lnum, char ope, int rnum)
{
if (ope == '+')
return lnum + rnum;
if (ope == '-')
return lnum - rnum;
if (ope == '*')
return lnum * rnum;
if (ope == '/')
return lnum / rnum;
}
/*
1+2*3=
1*(2+1*(3+5)+4*3)=
先乘除，后加减，有括号先算括号内的
1+5*4-345+36/6*4+145*4*5-52=
*/
void do_arithmetic()
{
stack_int s;
stack_int num_stack;//数据栈
stack_int ope_stack;//符号栈
char current_char;
current_char = getchar();
bool overflag = false;//结束标志
bool errorflag = false;//出错标志
while (overflag != true)
{//未遇到=号时不断进行四则运算
if (is_digit(current_char))
{//遇到数字符号则将完整的数解析出来并保存于栈中
int num = 0;
num = current_char - '0';//符号转数字
current_char = getchar();//获取下一个字符
while (is_digit(current_char))
{
num = num * 10 + (current_char - '0');
current_char = getchar();
}
num_stack.push(num);
//cout <<"the number is " <<num << endl;
}
if (current_char == ' '||current_char=='
')
{//空格或换行则继续
current_char = getchar();
continue;
}
if (is_operator(current_char))
{//遇到运算符则将运算符保存于运算符栈中
int ope = '?';
//如果当前符号栈非空，则不断根据优先级决定是否进行一次运算
while ((!ope_stack.isEmpty()) && (get_priority((char)ope_stack.gettop(), current_char)))
{//如果前一个运算符优先级更高
ope_stack.pop(ope);
//cout << "找到了前一个运算符为: " << (char)ope << endl;
int lnum, rnum;
//符号栈非空时，数据栈应该至少有两个数，否则出错
if (num_stack.isEmpty())
{
cout << "error: 数据栈缺失两个元素，解析失败！" << endl;
errorflag = true;
overflag = true;
break;
}
num_stack.pop(rnum);
if (num_stack.isEmpty())
{
cout << "error: 数据栈缺失一个元素，解析失败！" << endl;
errorflag = true;
overflag = true;
break;
}
num_stack.pop(lnum);
lnum = do_operation(lnum, (char)ope, rnum);//进行运算
num_stack.push(lnum);
}
if (current_char == '=')
{//如果解析到=号了,解析完成
if (!ope_stack.isEmpty())
{
errorflag = true;
cout << "error: 缺失)" << endl;
}
overflag = true;
break;
}
ope_stack.push(current_char);
if (current_char == ')')
{//右括号则出栈两次，将右括号和匹配的左括号出栈
ope_stack.pop(ope);
if (ope_stack.isEmpty())
{
cout << "error: 没有与)相匹配的(" << endl;
errorflag = true;
overflag = true;
break;
}
ope_stack.pop(ope);
}
current_char = getchar();
}
}
//for (int i = 0; i < num_stack.getsize(); ++i)
// cout << num_stack[i] << " ";
//cout << endl;
//for (int i = 0; i < ope_stack.getsize(); ++i)
// cout << (char)ope_stack[i] << " ";
if (!errorflag)
cout << num_stack.gettop() << endl;
}
int main()
{
cout << " ______________" << endl;
cout << "|整数四则运算器|" << endl;
cout << " --------------" << endl;
cout << "功能介绍：进行整数表达式的四则运算" << endl;
cout << "可以使用的运算符:+ - * /" << endl;
cout << "使用方式:输入以=结尾的算数运算表达式,回车后即可得到运算结果" << endl;
cout << endl;
//2432+5423-534*42=
while (true)
{
cout << "____________________" << endl;
cout << "--------------------" << endl;
cout << "> ";
do_arithmetic();
}
return 0;
}
程序大部分与不带括号版本很相似，主要更改了两个方面：
1.对于左括号，令左括号左边运算符优先级低于左括号，右边运算符优先级高于左括号(即，只要含有左括号的比较结果均为无法进行运算，函数get_priority返回值永远为false)。
2.对于右括号，令右括号左边的运算符(除左括号外)优先级均高于右括号，并且当右括号左边的符号为左括号时，两个括号相抵消，左括号退栈。
遇到右括号时，两括号内的+-*/运算全部可以进行，直到符号栈栈顶为左括号。