C++ 常量字符

Posted 2023-02-25

【中文标题】C++ 常量字符

【英文标题】：C++ Constant char

【发布时间】：2013-05-08 03:10:06

【问题描述】：

我用 c++ 构建了一个简单的计算器，它使用字符，因此 (+,-*,/) 可以用作数学运算符，但是当用户输入“=”时它就不起作用了。

#include <iostream>
#include <string>
#include <sstream>
#include <math.h>  
using namespace std;

#define PI 3.14159265359
#define NEWLINE '\n' 


void printf(string string)
 
  cout << string;


int main ()

char operation;
double a,b,c, value;
double answer = 0;
bool more = true;

cout << "Welcome to My Calculator\n\nInput a value: ";
cin >> answer;
operations:

cin >> operation;

if (operation != '=') 
    if (operation == '+') 
        cin >> value;
        cout << "\n" << answer << " " << operation << " " << value << "\n";
        answer += value;
        cout << "Equals " << answer << "\n";
        cout << answer << " - New Operation? ";
        goto operations;
    
    if (operation == '-') 
            cin >> value;
            cout << "\n" << answer << " " << operation << " " << value << "\n";
            answer -= value;
            cout << "Equals " << answer << "\n";
            cout << answer << " - New Operation? ";
            goto operations;
        
    if (operation == '*') 
            cin >> value;
            cout << "\n" << answer << " " << operation << " " << value << "\n";
            answer *= value;
            cout << "Equals " << answer << "\n\n";
            cout << answer << " - New Operation? ";
            goto operations;
        
    if (operation == '/') 
                cin >> value;
                cout << "\n" << answer << " " << operation << " " << value << "\n";
                answer /= value;
                cout << "Equals " << answer << "\n\n";
                cout << answer << " - New Operation? ";
                goto operations;
            
    if (operation == '^') 
                    cin >> value;
                    cout << "\n" << answer << " " << operation << " " << value << "\n";
                    answer = pow(answer, value);
                    cout << "Equals " << answer << "\n\n";
                    cout << answer << " - New Operation? ";
                    goto operations;
                
    if (operation == '=') 
                    cout << "\nFinal Answer = " << answer << "\n\nNew operation [yes/no]: ";
                    string check;
                    cin >> check;
                    if (check == "yes") 
                        cout << "\nInput value: ";
                        cin >> answer; 
                        cout << "\n";
                        goto operations;
                     else 
                        cout << "\nGoodbye for now...\n";
                        return 0;
                    

                
 else 
    cout << "Unknown Error! Program Closing...";
    return 0;



return 0;

当用户使用除 = 之外的任何操作时，它都能正常工作，但如果我使用和等号，它就不起作用了。

示例程序输出：

Welcome to My Calculator

Input a value: 4
+4

4 + 4
Equals 8
8 - New Operation? - 3

8 - 3
Equals 5
5 - New Operation? * 5

5 * 5
Equals 25

25 - New Operation? /2

25 / 2
Equals 12.5

12.5 - New Operation? ^2

12.5 ^ 2
Equals 156.25

156.25 - New Operation? =
Unknown Error! Program Closing...

【问题讨论】：

if (operation != '=') ... if (operation == '=')

这不应该编译，因为这行：operations。那里没有冒号，而且循环更适合。

@user2371751：对试图帮助修复您的程序的人说“它不起作用”就像去看医生并告诉他“我感觉不好”——仅此而已。

【参考方案1】：

if (operation != '=') 
    ...
    if (operation == '=') 
    

如果运算不等于“=”并且等于“=”。我认为您计划在第一个外部 if 中放置一个 闭包运算符 或类似的东西。

【参考方案2】：

您的语句 if (operation != '=') 导致控制权转移到 else 语句

【参考方案3】：

因为您在检查 = 的 if 之外有一个 if (operation != '=')。你不想那样做。