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我能够解决这个问题的唯一方法是创建全局变量float x, y;，然后在整个程序中使用它们。我对编程很陌生，因为这很明显，但我听说创建全局变量通常是一种不好的做法。

我的猜测是问题出现在void completeOperation(int z){}函数中，因为错误消息基本上表明变量 x 和 y 都没有被声明。当我在该范围内声明它们时，它要求我给它们一个值，而我需要用户在 main.xml 中输入所述值。

我怎样才能使这项工作？原谅我不得不把整个代码放上去。它很小。

#include <iostream>
using namespace std;         
void createMenu();
void completeOperation(int z);
float add(float x, float y);
float subtract(float x, float y);
float multiply(float x, float y);
float divide(float x, float y);
float greaterNumber(float x, float y);
float lesserNumber(float x, float y);

int main()
{
    float x, y;

    cout << "Enter the first real number value." << endl;
    cin >> x;
    cout << "Enter the second real number value." << endl;
    cin >> y;

    createMenu();
    int z;
    cin >> z;

    completeOperation(z);

    system("pause");
}

void createMenu()
{
    cout << "\nChoose a desired arithmetic operation by entering a number from 1 to 6. \n\n";
    cout << "1.) Addition \n2.) Subtraction \n3.) Multiplication \n4.) Division \n5.) Bigger number \n6.) Smaller number" << endl;
}

void completeOperation(int z)
{
    switch (z)
    {
    case 1:
        cout << "\nAddition: " << add(x, y) << endl;
        break;
    case 2:
        cout << "\nSubtraction: " << subtract(x, y) << endl;
        break;
    case 3:
        cout << "\nMultiplication: " << multiply(x, y) << endl;
        break;
    case 4:
        cout << "\nDivision: " << divide(x, y) << endl;
        break;
    case 5:
        cout << "\nBigger number: " << greaterNumber(x, y) << endl;
        break;
    case 6:
        cout << "\nSmaller number: " << lesserNumber(x, y) << endl;
        break;
    }
}

float add(float x, float y)
{
    return (x + y);
}
float subtract(float x, float y)
{
    return (x - y);
}
float multiply(float x, float y)
{
    return (x * y);
}
float divide(float x, float y)
{
    return (x / y);
}
float greaterNumber(float x, float y)
{
    if (x > y)
    {
        return x;
    }
    else return y;
}
float lesserNumber(float x, float y)
{
    if (x < y)
    {
        return x;
    }
    else return y;
}
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