c++ - 重新定义一个int错误

Question

我正在自学 C++，我意识到这个问题对某些人来说似乎是补救措施。在我制作的游戏中，作为学习过程的一部分，我希望用户能够选择一个困难，当他们选择一个或另一个时，随机数值范围会发生变化。顺便说一下，我使用的编译器是 x-Code。这是代码:

#include <iostream>
#include <cstdlib>
#include <ctime>

using namespace std;

int secretNumber;

int main() //integrate difficulty chooser where easy is a number b/w 1 and 10, norm 1 and 50, and hard is 1 and 100
{
    srand(static_cast<unsigned int>(time(0))); //seeds random number by time read on system

    int guess;
    int choice;

    char again = 'y';

    cout << "\tWelcome to Guess My Number\n\n";
    cout << "Please choose a difficulty:\n";
    cout << "1 - Easy\n";
    cout << "2 - Normal\n";
    cout << "3 - Hard\n";
    cin >> choice;

    while (again =='y')
    {
        int tries = 0;
        int secretNumber;
        do
        {                
            cout << "Enter a guess: ";
            cin >> guess;
            ++tries;

            switch (choice)
            {
                case 1:
                    cout << "You picked Easy.\n";
                    int secretNumber = rand() % 10 + 1;
                    break;            
                case 2:
                    cout << "You picked Normal.\n";
                    int secretNumber = rand() % 50 + 1;
                    break;
                case 3:
                    cout << "You picked Hard.\n";
                    int secretNumber = rand() % 100 + 1;
                    break;                    
                default:
                    cout << "You have made an illegal choice.\n";
            }

            if (guess > secretNumber)
            {
                cout << "\nToo high!";
            }
            else if (guess < secretNumber)
            {
                cout << "\nToo low!";
            }
            else if (guess == secretNumber && tries == 1)
            {
                cout << "\nThat's unbelievable! You guessed it in exactly 1 guess";
            }
            else
            {
                cout << "\nGreat job, you got it in just " << tries << " guesses!\n";
            }

        }
        while(guess != secretNumber);

        cout << "Do you want to play again y/n: ";
        cin >> again;
    }

    return 0;

}

这 2 个错误发生在情况 2 和情况 3 中，我尝试重新定义 secretNumber 的值。

Answer 1

case block 不会打开不同的范围，而是同一个 block 的一部分。您的代码(仅考虑范围)看起来有点类似于:

int secretNumber;
{
int secretNumber = rand() %  10 + 1;
...
int secretNumber = rand() %  50 + 1;
...
int secretNumber = rand() % 100 + 1; 
}

在同一个作用域中声明了三个同名的不同变量，这在语言中是不允许的。请注意，switch 中的所有三个声明也会隐藏在外部作用域中声明的变量，这可能不是您想要的。