C++实现四则运算器(带括号)

 更新时间:2020年11月25日 14:21:57   作者:shadowgully  
这篇文章主要为大家详细介绍了C++实现四则运算器,文中示例代码介绍的非常详细,具有一定的参考价值,感兴趣的小伙伴们可以参考一下

本文实例为大家分享了C++实现四则运算器的具体代码,供大家参考,具体内容如下

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=='\n')
 {//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] << "\t";
 //cout << endl;
 //for (int i = 0; i < ope_stack.getsize(); ++i)
 // cout << (char)ope_stack[i] << "\t";
 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。

以上就是本文的全部内容,希望对大家的学习有所帮助,也希望大家多多支持脚本之家。

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