在C++中使用數組進行多項選擇測試的困惑

Question

對於我來說，我負責創建一個具有一組預先給定的正確答案的多項選擇測試。提示用戶輸入20個答案，然後該程序應該將正確的答案與學生輸入的答案進行比較。我很困惑重寫數組的大小，因爲我試圖將所有學生的正確和不正確答案放入兩個新數組中，然後輸出給用戶以查看他/她得到的正確答案。

我的代碼是：

#include<iostream> 
#include<string> 
using namespace std; 

int main() 
{ 
char answers[20] = { 'A','D','B','B','C','B','A','B','C','D','A','C','D','B','D','C','C','A','D','B' }; 
char studentAnswers[20]; 
int correctlyAnswered[20]; 
int falselyAnswered[20]; 
for (int i = 0; i <= 19; i++) 
{ 
    cout << "Please enter your answer for question #" << i+1 << ": "; 
    char choice; 
    cin >> choice; 
    if (choice != 'A' || choice != 'B' || choice != 'C' || choice != 'D') 
    { 
     cout << "Error: Answer must be A,B,C or D. Please enter a new answer: "; 
     cin >> choice; 
    } 
    studentAnswers[i] = choice; 
    cin.sync(); 
    if (answers[i] = studentAnswers[i]) 
    { 
     studentAnswers[i] = correctlyAnswered[i]; 
    } 
    else 
    { 
     studentAnswers[i] = falselyAnswered[i]; 
    } 


} 
cout << "You answered " << sizeof(correctlyAnswered[20]) << " questions correctly out of 20" << endl; 
system("pause"); 
return 0; 

}

代碼心不是完全完成，但我想出來繼續之前解決這問題。我相信我的問題源於將正確答覆和falselyAsnswered陣列的大小設置爲20，但我不確定該如何解決此問題。請幫忙！

Answer 1

我建議每增加學生正確回答時間int。

因此，我將修改代碼聲明：

int correctlyAnswered = 0; 

然後在for週期我想：

if (answers[i] == choice) 
    correctlyAnswered++; 

（注意：==沒有=）
最後，你可以輸出：

cout << "You answered " << correctlyAnswered << " questions correctly... 

點

其他一些建議：
- 使用while週期來獲取用戶輸入

while(1) { 
    cin >> choice; 
    if (choice != 'A' || choice != 'B' || choice != 'C' || choice != 'D') 
    cout << "Error: Answer must be A,B,C or D. Please enter a new answer: "; 
    else 
    break; 
} 

• 計算falselyAnswered：

  falselyAnswered = 20 - correctlyAnswered;

更新 爲了將sutdent答案正確的存儲問題，我將宣佈一個布爾值數組：

int correctlyAnswered = 0; 
bool correct[20]; 

然後修改，如果：

if (answers[i] == choice) { 
    correctlyAnswered++; 
    correct[i] = true; 
} else { 
    correct[i] = false; 
} 

然後打印出結果：

cout << "You answered " << correctlyAnswered << " questions correctly"<<endl; 
for(int i=0; i<20; i++) { 
    count << "Your answer to question " << i+1 << " is "; 
    if (correct[i]) 
     cout << "correct" << endl; 
    else 
     cout << "wrong" << endl; 
} 

Answer 2

您的代碼有幾個問題。第一招：

if (answers[i] = studentAnswers[i]) 

這就賦予answers[i]到studentAnswers[i]。你想使用== - 這是一個比較運算符。

然後，

studentAnswers[i] = correctlyAnswered[i]; 

並沒有真正意義。 correctlyAnswered是一個單元數據的數組，你爲什麼從它讀取任何東西？我假設，你想以某種方式設置studentAnswers[i]。

cout << "You answered " << sizeof(correctlyAnswered[20]) << " 

sizeof(studentAnswersed[20])總是返回相同的值，也就是char大小，它總是存在保證爲1

Answer 3

我想這不是真正的問題，但我們都在這裏幫忙。你的問題是一個很基本的一個：

if (answers[i] = studentAnswers[i]) 

由於沒有分配和比較，C++之間的差異采用不同的運營商這一點。 （你必須習慣它），而不是使用一個單一的平等，比較是一個雙等號==

在這個例子中，你正在測試的任務。所以你分配studentAnswer回答，比檢查分配的東西是否與false不同（或者在這種情況下'\ 0'）

我不知道你使用的是哪個編譯器和IDE，對此的警告：使用賦值結果作爲沒有括號的條件

這就是說，請停止編寫C. STL具有數組和矢量的容器。結合基於範圍的算法，...這段代碼將更容易理解。

Answer 4

首先，您必須使用'=='而不是'='第一個是比較運算符，用於評估兩個聲明是否相等，第二個是將一個變量的值賦值給另一個的賦值運算符。

其次，您必須在您評估正確答案時交換順序。相反的：

if (answers[i] = studentAnswers[i]) 
{ 
    studentAnswers[i] = correctlyAnswered[i]; 
} 
else 
{ 
    studentAnswers[i] = falselyAnswered[i]; 
} 

你要做這樣的：

if (answers[i] = studentAnswers[i]) 
{ 
    correctlyAnswered[i] = studentAnswers[i]; 
} 
else 
{ 
    falselyAnswered[i] = studentAnswers[i]; 
} 

三，聲明的sizeof（correctlyAnswered [20]）將始終輸出80，that's bacause的sizeof（）返回大小以字節爲單位，在這種情況下爲80。

那麼，應該這樣做。

現在，如果你想顯示你應該增加這個好答案：

int correctNumbers[20] = {};//this initializes the 20 numbers with 0 

if語句

然後：

if (answers[i] = studentAnswers[i]) 
{ 
    correctlyAnswered[i] = studentAnswers[i]; 
    correctNumbers[i] = i + 1;//stores the number of the good answeded                             //question 
} 

最後以顯示：

cout << "You answeded well the next questions:\n" 
for(i = 0; i < 20; ++i) 
    if(correctNumber[i] != 0) 
     cout << correctNumber[i] << ' '; 

那工作，有一個更好的方法來解決這個問題，但是這對你正在努力解決的問題已經足夠了:)

Answer 5

我按如下格式化了最終代碼。

#include<iostream> 
#include<string> 
using namespace std; 

int main() 
{ 
char answers[20] = { 'A','D','B','B','C','B','A','B','C','D','A','C','D','B','D','C','C','A','D','B' }; 
char studentAnswers[20]; 
int correctlyAnswered = 0; 
bool correct[20]; 
int falselyAnswered[20]; 
for (int i = 0; i <= 19; i++) 
if (answers[i] == choice) 
    correctlyAnswered++; 
{ 
    cout << "Please enter your answer for question #" << i+1 << ": "; 
    char choice; 
    cin >> choice; 
    if (choice != 'A' || choice != 'B' || choice != 'C' || choice != 'D') 
    cout << "Error: Answer must be A,B,C or D. Please enter a new answer: "; 
    cin >> choice; 
    else 
    break; 
} else { 
    cout << "You answered " << correctlyAnswered << " questions correctly... 
    } 
    studentAnswers[i] = choice; 
    cin.sync(); 
    if (answers[i] == choice) { 
     correctlyAnswered++; 
     correct[i] = true; 
} else { 
     correct[i] = false; 
    } 

     studentAnswers[i] = correctlyAnswered[i]; 
    } 
    else 
    { 
     studentAnswers[i] = falselyAnswered[i]; 
    } 
     falselyAnswered = 20 - correctlyAnswered; 

} 
cout << "You answered " << correctlyAnswered << " questions correctly"<<endl; 
     for(int i=0; i<20; i++) { 
    count << "Your answer to question " << i+1 << " is "; 
     if (correct[i]) 
     cout << "correct" << endl; 
    else 
     cout << "wrong" << endl; 
} 

system("pause"); 
return 0;