每次調用變量時，如何生成隨機數字？

Question

我正在製作一個非常簡單的「數學導師」程序，我需要顯示一個帶有4個選項的菜單：加，減，乘和退出。該程序應循環，直到我選擇退出。

到目前爲止，一切似乎都在起作用，但我無法弄清楚每次程序循環時如何創建一個新的隨機數。

下面是代碼：

#include <iostream> 
#include <iomanip> 
#include <cstdlib> 
#include <ctime> 
using namespace std; 

int main() 
{ 
    int addFirstNum, 
    addSecondNum, 
    subFirstNum, 
    subSecondNum, 
    multFirstNum, 
    multSecondNum, 
    operNum, 
    num; 
    bool temBool = true; //Temporary boolean used in the while loop 
    unsigned seed; // Random generator seed 

    // Use the time function to get a "seed" value for srand 
    seed = time(0); 
    srand(seed); 

    //Random generated operands 
    addFirstNum = rand() % 40 + 10; 
    addSecondNum = rand() % 40 + 10; 
    subFirstNum = rand() % 40 + 10; 
    subSecondNum = rand() % 40 + 10; 
    multFirstNum = rand() % 40 + 10; 
    multSecondNum = rand() % 40 + 10; 


    while (temBool) //Start of the loop 
    { 
     // Menu of Math Tutor 
     cout << "Math Tutor - Main Menu"; 
     cout << endl << endl; 
     cout << "1. Adittion\n"; 
     cout << "2. Subtraction\n"; 
     cout << "3. Multiplication\n"; 
     cout << "4. Exit Program\n"; 
     cout << endl << endl; 
     cout << "Choose your operation to practice (1-4) "; 
     cin >> operNum; 
     cout << endl << endl; 

     // Switch for the menu's options 
     switch (operNum) 
     { 
      case 1: 
       cout << "Working with addition\n"; 
       cout << setw(3) << addFirstNum << "\n" 
       << "+" << addSecondNum << "\n" 
       << "---\n"; 
       cout << "Your answer: "; 
       cin >> num; 
       if(num == addFirstNum + addSecondNum) 
       { 
        cout << "Correct answer: " 
        << addFirstNum + addSecondNum << " Congratulations!\n"; 
       } 
       else 
       { 
        cout << "Correct answer: " 
        << addFirstNum + addSecondNum << " Sorry!\n"; 
       } 
       cout << endl << endl; 
       break; 
      case 2: 
       cout << "Working with subtraction\n"; 
       cout << setw(3) << subSecondNum << "\n" 
       << "-" << multFirstNum << "\n" 
       << "---\n"; 
       cout << "Your answer: "; 
       cin >> num; 
       if(num == subSecondNum - multFirstNum) 
       { 
        cout << "Correct answer: " 
        << subSecondNum - multFirstNum << " Congratulations!\n"; 
       } 
       else 
       { 
        cout << "Correct answer: " 
        << subSecondNum + multFirstNum << " Sorry!\n"; 
       } 
       cout << endl << endl; 
       break; 
      case 3: 
       cout << "Working with multiplication\n"; 
       cout << setw(3) << multFirstNum << "\n" 
       << "*" << multSecondNum << "\n" 
       << "---\n"; 
       cout << "Your answer: "; 
       cin >> num; 
       if(num == multFirstNum * multSecondNum) 
       { 
        cout << "Correct answer: " 
        << multFirstNum * multSecondNum << " Congratulations!\n"; 
       } 
       else 
       { 
        cout << "Correct answer: " 
        << multFirstNum + multSecondNum << " Sorry!\n"; 
       } 
       cout << endl << endl; 
       break; 
      case 4: 
       cout << "Thank you for using Math Tutor.\n"; 
       temBool = false; 

       break; 
      default: cout << "Incorrect menu seletion. Please choose between 1 and 4.\n"; 
       return 0; 
     } 
    } 
} 

Answer 1

簡單：

移動循環內的隨機數發生器線：

seed = time(0); 
srand(seed); //setting the seed should only be done outside the loop (as per original code) 

while (temBool) //Start of the loop 
{ 

    //Random generated operands 
    addFirstNum = rand() % 40 + 10; 
    addSecondNum = rand() % 40 + 10; 
    subFirstNum = rand() % 40 + 10; 
    subSecondNum = rand() % 40 + 10; 
    multFirstNum = rand() % 40 + 10; 
    multSecondNum = rand() % 40 + 10; 

    //... 
} 

現在每次循環的時候，該號碼將具有新的價值。

編輯：現在回答顯示srand(seed)明確地在循環之外，以防您的問題將代碼移入循環。
此外，就像whozcraig所說的，每次只需要兩個隨機數，因爲您只使用每次生成的兩個數字。

Answer 2

只是對Baldrick的一個補充答案，當你用時間（0）播種，然後只做一段時間循環，沒有任何停頓或詢問用戶下一步做什麼（退出/繼續）時，值將是相同的種子具有相同的時間值（時間值沒有改變，因爲while循環能夠快速處理程序）。也許這不是問題，但很好知道:)