c++ - If/else 循环 : C++ Program: Won't display final prompt/final loop

Question

我在第一门 C++ 类(class)的作业中遇到了很多麻烦。

我已经想出如何让它正确地询问用户他们想使用什么操作(加、减、乘)，生成 0-9 之间的随机数，以及如何要求用户解决问题和回答是对还是错。

在此之后，程序应该询问用户是想继续(按 y)还是退出(按 Q)，并在用户输入任何其他字母时向用户显示错误消息，但对于由于某些原因，这部分在运行程序时没有显示。

如何让循环正常工作，允许我执行最后的提示，然后仅在按 Y 时重复整个程序或在按 Q 时退出？

注意:总的来说，我对编码还很陌生，这是我的第一门 C++ 类(class)，所以我还不知道如何让这段代码更简洁:

#include <iostream>
#include <cstdio>
#include <time.h>
#include <stdlib.h>
using namespace std;

int main()

{
    while (true)
   {
  // Generate two random single-digit integers btwn 0-9
  srand(time(0));
  int num1 = rand() % 10;
  int num2 = rand() % 10;
  int operation, play, num3, guess, Y, Q;

  // If num1 < num2, swap num1 with num2
  if (num1 < num2)
  {
  int temp = num1;
  num1 = num2;
  num2 = temp;
  }

cout << "Choose an operation." << endl;
cout << "Enter 1 to add, 2 to subtract, or 3 to multiply: " << endl;
cin >> operation;

    if (operation > 3 || operation < 1)
    {
        cout << "Your operation choice isn't valid!  Please try again, using 1, 2, or 3." << endl;
        cout << "Choose an operation." << endl;
        cout << "Enter 1 to add, 2 to subtract, or 3 to multiply: " << endl;
        cin >> operation;
    }

     else if (operation == 1)
        {
        cout << "You chose addition." << endl;
        num3 = num1 + num2;
        cout << "What is " <<  num1 << " + " << num2 << " ?: " << endl;
        cin >> guess;

            if (guess != num3)
                {
                cout << "That is incorrect. Please try again." << endl;
                cout << "" << endl;
                cout << "What is " <<  num1 << " + " << num2 << " ?: " << endl;
                cin >> guess;
                }

            else if (guess == num3)
                {
                cout << "That is correct!" << endl;
                cout << "" << endl;
                }
        }

     else if (operation == 2)
        {
        cout << "You chose subtraction." << endl;
        num3 = num1 + num2;
        cout << "What is " <<  num1 << " - " << num2 << " ?: " << endl;
        cin >> guess;

            if (guess != num3)
                {
                cout << "That is incorrect. Please try again." << endl;
                cout << "" << endl;
                cout << "What is " <<  num1 << " - " << num2 << " ?: " << endl;
                cin >> guess;
                }

            else if (guess == num3)
                {
                cout << "That is correct!" << endl;
                cout << "" << endl;
                }
        }

     else if (operation == 3)
        {
        cout << "You chose multiplication." << endl;
        num3 = num1 * num2;
        cout << "What is " <<  num1 << " * " << num2 << " ?: " << endl;
        cin >> guess;

            if (guess != num3)
                {
                cout << "That is incorrect. Please try again." << endl;
                cout << "" << endl;
                cout << "What is " <<  num1 << " * " << num2 << " ?: " << endl;
                cin >> guess;
                }

            else if (guess == num3)
                {
                cout << "That is correct!" << endl;
                cout << "" << endl;
                }
        }

while (guess != num3)
         {
         int play, Y, Q;
         cout << "Would you like to play again? Press Y for yes or Q for 
quit" << endl;
         cin >> play;

           if (play != Y || play != Q)
            {
                cout << "That is not a valid choice. Please choose Y for yes 
or Q to quit. " << endl;
                cin >> play;
            }

            else
            {
                if (play == Y)
                {
                cout << "Thank you for playing! Let's play again!" << endl;
                cout << "" << endl;
                }


                else if (play == Q)
                {
                cout << "Thank you for playing! See you next time!" << endl;
                cout << "" << endl;
                }
                break;
                }
         }
         }
return 0;
}

Answer 1

这里有一些东西......

1。只播种一次

将 srand(time(0)); 移出 while 循环并移至 main 的顶部。如果您在同一秒内重复播种(如果 time(0) 不变)，您将两次获得相同的“随机”数字。

2。如果他们没有输入有效的操作，num3 会怎样？

你永远不会初始化 num3，所以如果他们没有选择有效的 operation，num3 就会有一个垃圾值。然后继续运行一个循环，其条件取决于 num3 的值! (while (guess != num3))

3。 else { ... if { 与 else if {

相同

在最后一个循环中，将 if (play == Y) 和 else if (play == Q) 带出嵌套的 if 并使它们成为 else if。

4。你最后的循环条件不正确

while (guess != num3) 真的对吗？你想循环直到他们输入有效输入，那么你为什么要循环 while guess != num3？