C++加减法计算器else if语句失效问题求助

我用C++编写了一款仅支持加减法的计算器，程序包含两个void函数：

• userInterface()：负责显示用户界面，让用户选择加法、减法运算或退出程序
• conditionals()：包含三个条件分支，前两个分支分别处理加减运算并输出结果，第三个分支处理无效输入并引导返回初始界面

目前遇到的问题是：当输入“2”或“2.”选择减法时，程序会触发第三个无效选项分支，输出“Invalid choice”；尝试删除第三个条件分支后，程序直接以退出码0结束，问题仍未解决。

原代码 #

#include <iostream>
#include <thread>

using namespace std;

float userInterfaceChoice;
float num1;
float num2;

void conditionals();

void userInterface()
{
    cout<<"CALCULATOR"<<endl
        <<""<<endl
        <<"Please choose an option"<<endl
        <<"1. Sum"<<endl
        <<"2. Subtraction"<<endl
        <<"3. Exit"<<endl;
    cin>>userInterfaceChoice;
    
    this_thread::sleep_for(1s);
    conditionals();
}


void conditionals()
{
    // Sum
    
    if(userInterfaceChoice==("1"||"1."))
    {
        // Input of numbers
        cout<<""<<endl
            <<"SUM"<<endl
            <<"Enter the first number"<<endl;
        cin >>num1;
        cout<<""<<endl
            <<"Enter the second number"<<endl;
        cin >>num2;
        
        // Operation & Output
        
        cout<<"The sum equals "<<num1+num2<<endl;
        
        // Wait 2 seconds, then come back to the GUI
        
        this_thread::sleep_for(2s);
        userInterface();
    }
    
    // Subtracion
    
    else if(userInterfaceChoice==("2"||"2."))
    {
        // Numbers input
        cout<<""<<endl
            <<"SUM"<<endl
            <<"Enter the first number"<<endl;
        cin >>num1;
        cout<<""<<endl
            <<"Enter the second number"<<endl;
        cin >>num2;
        
        // Operation & Output
        
        cout<<"The subtraction equals"<<num1-num2<<endl;
        
        // Wait 2 seconds, come back to the GUI
        
        this_thread::sleep_for(2s);
        userInterface();
    }
    
    //Invalid choice
    
     else if(userInterfaceChoice!=("1"&&"1."&&"2"&&"2."))
    {
        cout<<""<<endl
            <<"Invalid choice"<<endl;
        // Wait 2 seconds, come back to the GUI
        
        this_thread::sleep_for(2s);
        userInterface();
    }
}

// Execute the void functions

int main()
{
    userInterface();
    conditionals();
}

问题分析 #

核心问题集中在条件判断逻辑错误和变量类型不匹配：

1. userInterfaceChoice是float类型，却和字符串字面量"1"、"2"比较，C++中会将字符串指针转换为数值，结果完全不符合预期
2. 逻辑运算符使用错误：("1"||"1.")实际是判断两个字符串指针是否非空，结果永远为true，转换成数值后和1.0巧合匹配，但("2"||"2.")同样为true，转换数值后不等于2.0，导致减法分支永远不触发
3. 第三个分支的!=("1"&&"1."&&"2"&&"2.")逻辑完全错误，&&连接字符串指针判断非空，结果为true，几乎所有情况都会触发无效分支
4. main()中重复调用conditionals()，userInterface()内部已经调用过该函数，导致逻辑冗余

修正后的代码 #

#include <iostream>
#include <thread>
#include <chrono>

using namespace std;

int userInterfaceChoice;
float num1;
float num2;

void conditionals();

void userInterface()
{
    cout << "CALCULATOR" << endl
         << endl
         << "Please choose an option" << endl
         << "1. Sum" << endl
         << "2. Subtraction" << endl
         << "3. Exit" << endl;
    cin >> userInterfaceChoice;

    this_thread::sleep_for(chrono::seconds(1));
    conditionals();
}

void conditionals()
{
    // 加法分支
    if(userInterfaceChoice == 1)
    {
        cout << endl
             << "SUM" << endl
             << "Enter the first number" << endl;
        cin >> num1;
        cout << endl
             << "Enter the second number" << endl;
        cin >> num2;

        cout << "The sum equals " << num1 + num2 << endl;

        this_thread::sleep_for(chrono::seconds(2));
        userInterface();
    }
    // 减法分支
    else if(userInterfaceChoice == 2)
    {
        cout << endl
             << "SUBTRACTION" << endl;
        cout << "Enter the first number" << endl;
        cin >> num1;
        cout << endl
             << "Enter the second number" << endl;
        cin >> num2;

        cout << "The subtraction equals " << num1 - num2 << endl;

        this_thread::sleep_for(chrono::seconds(2));
        userInterface();
    }
    // 退出分支
    else if(userInterfaceChoice == 3)
    {
        cout << endl << "Exiting program..." << endl;
        return;
    }
    // 无效选项分支
    else
    {
        cout << endl
             << "Invalid choice" << endl;
        this_thread::sleep_for(chrono::seconds(2));
        userInterface();
    }
}

int main()
{
    userInterface();
    return 0;
}

修正说明 #

• 将userInterfaceChoice改为int类型，匹配选项的整数属性，避免浮点比较的精度问题
• 修正条件判断：直接用整数1、2、3和选项变量比较，去掉错误的字符串比较和逻辑运算符
• 补充选项3的退出逻辑，原代码未处理退出分支
• 修正减法分支中错误的标题（原代码误写为SUM）
• 移除main()中多余的conditionals()调用，避免重复执行
• 改用chrono::seconds(1)替代1s，提升代码兼容性

内容的提问来源于stack exchange，提问作者Elrichiz