C++字符串程序导致的运行时错误

Question

我正在用 C++ 创建这个程序，它要求用户输入带有大写和小写字母的电影标题。它确定并显示标题中大小写字母的数量。然后它创建 3 个字符串，将原始字符中的所有字符转换为大写，然后转换为小写，然后转换为相反的大小写。它分别显示这些字符串。在显示大小写字母的数量后出现问题。程序输出一条错误消息，说明它必须请求运行时以不寻常的方式终止它。我需要一些帮助来识别问题并解决它。谢谢 这是我的代码：

#include <cstdlib>
#include <iostream>
#include <string>
#include <cctype>

using namespace std;

int main(int argc, char *argv[])
{
    string title, upper, lower, swap;
    int upCount = 0, lowCount = 0;

    cout << "Please enter your favorite movie title:\n(it should have upper and lowercase letters)" << endl;
    getline(cin, title);
    for (int i = 0; i < title.size(); i++)
    {
        if (isupper(title.at(i)))
            upCount++;
        else if (isalpha(title.at(i)))
            lowCount++;
    }
    cout << title << " has " << upCount << " uppercase letters and " << lowCount << " lowercase letters." << endl;
    for (int i = 0; i < title.size(); i++)  
    {    
         upper.at(i) = title.at(i);
         lower.at(i) = title.at(i);
         swap.at(i) = title.at(i);
    }
    for (int i = 0; i < title.size(); i++)
    {
         if (isupper(title.at(i)))
             swap.at(i) = tolower(int(swap.at(i)));
         else
             swap.at(i) = toupper(int(swap.at(i)));
         upper.at(i) = toupper(int(upper.at(i))); 
         lower.at(i) = tolower(int(lower.at(i)));
    }
    cout << upper << endl
         << lower << endl
         << swap << endl;

    system("PAUSE");
    return EXIT_SUCCESS;
}

Answer 1

您永远不会将upper、lower 或swap 初始化为任何值。当您执行upper.at(i)、lower.at(i) 或swap.at(i) 时，程序将中断。

您可以通过在第二个循环之前将upper、lower 和swap 全部设置为title 来解决此问题。

变化：

...
    cout << title << " has " << upCount << " uppercase letters and " << lowCount << " lowercase letters." << endl;
    upper = lower = swap = title; //Add this
    for (int i = 0; i < title.size(); i++)
...

输出：

Please enter your favorite movie title:
(it should have upper and lowercase letters)
V for Vendetta
V for Vendetta has 2 uppercase letters and 10 lowercase letters.
V FOR VENDETTA
v for vendetta
v FOR vENDETTA