在這個 if 語句中使用計數每個不同值連續出現多少次，為什么它不打印最終值？

Question

此示例來自 c++ 入門第 5 版，使用 if 編寫程序來計算每個不同值在輸入中連續出現的次數

如果我們給這個程序以下輸入：

42 42 42 42 42 55 55 62 100 100 100

那么 output 應該是

42 occurs 5 times
55 occurs 2 times
62 occurs 1 times
100 occurs 3 times

但是當我嘗試時，它不會打印最后一個值或計數。 這是代碼：

  #include <iostream>
  int main()
  {
       // currVal is the number we're counting; we'll read new values into val
       int currVal = 0, val = 0;
       // read first number and ensure that we have data to process
       if (std::cin >> currVal) {
          int cnt = 1; // store the count for the current value we're processing
          while (std::cin >> val) { // read the remaining numbers
              if (val == currVal) // if the values are the same
                 ++cnt; // add 1 to cnt
              else { // otherwise, print the count for the previous value
                 std::cout << currVal << " occurs "
                           << cnt << " times" << std::endl;
                 currVal = val; // remember the new value
                 cnt = 1; // reset the counter
             }
          }   // while loop ends here
           // remember to print the count for the last value in the file
          std::cout << currVal << " occurs "
                    << cnt << " times" << std::endl;
       } // outermost if statement ends here
       return 0;
    }

Answer 1

正如上面提到的那樣，您可以使用 Ctrl+D 或者您可以使用以下語句，例如：如果用戶輸入 -1，則循環中斷。

我已將該語句添加到您的代碼中

#include <iostream>
int main()
{
    // currVal is the number we're counting; we'll read new values into val
    int currVal = 0, val = 0;
    // read first number and ensure that we have data to process
    std::cout << "-1 to exit\n";
    if (std::cin >> currVal) {
        int cnt = 1; // store the count for the current value we're processing
        while (std::cin >> val && val != -1) { // read the remaining numbers
            if (val == -1) // if the user enters -1 the loop breaks
                break;
            else if (val == currVal) // if the values are the same
                ++cnt; // add 1 to cnt
            else { // otherwise, print the count for the previous value
                std::cout << currVal << " occurs "
                    << cnt << " times" << std::endl;
                currVal = val; // remember the new value
                cnt = 1; // reset the counter
            }
        }   // while loop ends here
         // remember to print the count for the last value in the file
        std::cout << currVal << " occurs "
            << cnt << " times" << std::endl;
    } // outermost if statement ends here
    return 0;
}