在課上一個半小時寫出來的，還望各位不吝賜教~

首先百度百科上抄一下定義：字尾表示式，指的是不包含括號，運算子放在兩個運算物件的後面，所有的計算按運算子出現的順序，嚴格從左向右進行（不再考慮運算子的優先規則）。

計算過程是這樣的：建立一個棧S 。從左到右讀表示式，如果讀到運算元就將它壓入棧S中，如果讀到n元運算子(即需要引數個數為n的運算子)則取出由棧頂向下的n項按運算元運算，再將運算的結果代替原棧頂的n項，壓入棧S中 。如果字尾表示式未讀完，則重複上面過程，最後輸出棧頂的數值則為結束。

這次課堂練習的時候助教說最好自己對棧進行一個實現。那麼我也就用了自己實現的棧。

MyStack.h

#ifndef MYSTACK_H_INCLUDED
#define MYSTACK_H_INCLUDED

#include <iostream>
#include <stdlib.h>

using namespace std;

enum Error_code{underflow, overflow, success};

const int maxStack = 100;

template<class Stack_entry>
class MyStack {

public:
    MyStack();
    bool empty() const;
    Error_code pop();
    Error_code top(Stack_entry &item) const;
    Error_code push(const Stack_entry &item);

private:
    int count_;
    Stack_entry entry[maxStack];
};

#endif // MYSTACK_H_INCLUDED
 

MyStack.cpp

#include "MyStack.h"

template<class Stack_entry>
MyStack<Stack_entry>::MyStack()
{
    count_ = 0;
}

template<class Stack_entry>
bool MyStack<Stack_entry>::empty() const
{
    return (count_ == 0);
}

template<class Stack_entry>
Error_code MyStack<Stack_entry>::pop()
{
    if (count_ < 1) {
        return underflow;
    }
    else {
        count_--;
        return success;
    }
}

template<class Stack_entry>
Error_code MyStack<Stack_entry>::top(Stack_entry &item) const
{
    if (count_ < 1) {
        return underflow;
    }
    else {
        item = entry[count_ - 1];
        return success;
    }
}

template<class Stack_entry>
Error_code MyStack<Stack_entry>::push(const Stack_entry &item)
{
    if (count_ >= maxStack) {
        return overflow;
    }
    else {
        entry[count_++] = item;
        return success;
    }
}
 

PolishCal.h

#ifndef POLISHCAL_H_INCLUDED
#define POLISHCAL_H_INCLUDED

#include "MyStack.h"
#include <math.h>

template<class Stack_entry>
class PolishCal {

public:
    void introduction();
    void instructions(MyStack<Stack_entry> &numbers);
    char get_command();
    bool do_command(char command, MyStack<Stack_entry> &numbers);

};

#endif // POLISHCAL_H_INCLUDED

PolishCal.cpp

#include "PolishCal.h"

template<class Stack_entry>
void PolishCal<Stack_entry>::introduction()
{
    cout << "This is a reverse Polish Calculator." << endl;
    cout << "Please enter a valid command:" << endl;
    cout << "[?]push to stack  [=]print top" << endl;
    cout << "[+] [-] [*] [/] [^] are arithmetic operations" << endl;
    cout << "[Q]quit" << endl;
}

template<class Stack_entry>
void PolishCal<Stack_entry>::instructions(MyStack<Stack_entry> &numbers)
{
    char input;
    input = get_command();
    while (input != 'Q' && input != 'q') {
        do_command(input, numbers);
        input = get_command();
    }
}

template<class Stack_entry>
char PolishCal<Stack_entry>::get_command()
{
    char input;
    cout << "Select command and press <Enter>:";
    cin >> input;
    cin.clear();
    cin.sync();
    while (input != '?' && input != '=' && input != '+' && input != '-' && input != '*' && input != '/' && input != '^' && input != 'Q' && input != 'q') {
        cout << "Input error. Please input again:";
        cin >> input;
        cin.clear();
        cin.sync();
    }
    return input;
}

template<class Stack_entry>
bool PolishCal<Stack_entry>::do_command(char command, MyStack<Stack_entry> &numbers)
{
    Stack_entry num;
    Stack_entry top;
    Stack_entry a, b;

    switch (command)
    {
    case '?':
        cout << "Enter a real number: ";
        cin >> num;
        numbers.push(num);
        break;
    case '=':
        numbers.top(top);
        cout << top << endl;
        break;
    case '+':
        numbers.top(a);
        numbers.pop();
        numbers.top(b);
        numbers.pop();
        numbers.push(a + b);
        break;
    case '-':
        numbers.top(a);
        numbers.pop();
        numbers.top(b);
        numbers.pop();
        numbers.push(b - a);
        break;
    case '*':
        numbers.top(a);
        numbers.pop();
        numbers.top(b);
        numbers.pop();
        numbers.push(a * b);
        break;
    case '/':
        numbers.top(a);
        numbers.pop();
        numbers.top(b);
        numbers.pop();
        numbers.push(b / a);
        break;
    case '^':
        numbers.top(a);
        numbers.pop();
        numbers.top(b);
        numbers.pop();
        numbers.push(pow(b, a));
        break;
    case 'Q':
    case 'q':
        break;
    default:
        break;
    }

    return true;
}

main.cpp

#include "MyStack.cpp"
#include "PolishCal.cpp"

int main(void)
{
    MyStack<double> stored_numbers;
    PolishCal<double> c;
    c.introduction();
    c.instructions(stored_numbers);
    return 0;
}

執行結果和老師給的PPT一樣~我就直接貼鮑哥的圖了