防止重复进入矢量？ C++

Question

我有一个程序，提示用户输入一个值。用户输入的每个值都放入一个向量'other'中，这个值只用于验证。如果输入了重复值，则用户将得到一个提示，直到他们输入唯一值。

我面临的主要问题是，由于某些原因，在运行代码并打印出矢量结果时，似乎有重复条目。谁能告诉我为什么？

请参阅以下我的代码：

// prompt to continue 
cout << "Would you like to continue? [Y]es, [N]o: "; 
cin >> toContinue; 

while (toContinue == 'Y') 
{ 
    bool isDuplicate = 0; 

    // prompt for product no. 
    cout << "Please enter product number: "; 
    cin >> productB; 

    // Validation check for duplicate entries 
    for (size_t i = 0; i < other.size(); i++) 
    { 
     if (productB == other[i]) 
      isDuplicate = 1; 

     while (isDuplicate == 1) 
     { 
      cout << "You have already entered this product number!" << endl; 
      cout << "Please enter correct product number: "; 
      cin >> productB; 

      if (productB != other[i]) 
       other.push_back(productB); 

      isDuplicate = 0; 
     } 
    } 
    // prompt to continue 
    cout << "Would you like to continue? [Y]es, [N]o: "; 
    cin >> toContinue; 
} 

Answer 1

虽然它通常使用std::set独特的元素，如果函数必须返回一个矢量由于某些原因，我用这样的方法：

std::set<int> my_set; 

my_set.insert(1); 
my_set.insert(2); 
my_set.insert(1); 

// ... insert more 

std::vector<int> my_vector(my_set.size()); 
std::copy(my_set.begin(), my_set.end(), my_vector.begin()); 

assert(my_vector.size()==2); 

请注意，矢量my_vector将被排序。

Answer 2

一旦你输入一个副本，你让用户重新输入一个数字;那么你只检查新输入的号码是否与之前输入的重复相同;但是您不检查用户是否输入了不同但仍然重复的值。

通常，您将用户输入与程序逻辑混合;分拆这使得代码更具可读性并且不易出错。参见，例如，下面的片段示出了如何人们可以分离这些顾虑：

bool isContained(const vector<int> &v, int value) { 
    // your code to check for duplicates goes here 
} 

int main() { 

    ... 

    while (toContinue == 'Y') { 

     // prompt for product no. 
     cout << "Please enter product number: "; 
     cin >> productB; 

     if (isContained(other, productB)) { 
     cout << "You have already entered this product number!" << endl; 
     } 
     else { 
     other.push_back(productB); 
     } 

     // prompt to continue 
     cout << "Would you like to continue? [Y]es, [N]o: "; 
     cin >> toContinue; 
    } 
} 

而且一般暗示：使用适当的数据结构还可以帮助避免码的不必要的行;例如，避免重复的容器是std::set。

Answer 3

您可以通过将逻辑组件分解为更小的函数来帮助自己。

我在这里完成的大部分工作都已经整理完毕，但请注意contains函数的封装。

#include <vector> 
#include <iostream> 
#include <algorithm> 

using namespace std; 

bool contains(std::vector<int> const& vals, int val) 
{ 
    return std::count(std::begin(vals), std::end(vals), val) != 0; 
} 

bool shouldContinue() 
{ 
    char toContinue; 
    cout << "Would you like to continue? [Y]es, [N]o: "; 
    cin >> toContinue; 
    return toContinue == 'Y'; 
} 

int getProduct(bool again) 
{ 
    int productB; 
    if (again) 
    { 
     cout << "You have already entered this product number!" << endl; 
    } 
    cout << "Please enter correct product number: "; 
    cin >> productB; 
    return productB; 
} 

void printProducts(std::vector<int> const& vals) 
{ 
    std::cout << "You have selected:"; 
    const char* sep = " "; 
    for(int p : vals) 
    { 
     std::cout << sep << p; 
     sep = ", "; 
    } 
    std::cout << std::endl; 
} 


int main() 
{ 
    std::vector<int> other; 

    while (shouldContinue()) 
    { 
     int productB = getProduct(false); 
     while(contains(other, productB)) 
     { 
      productB = getProduct(true); 
     } 
     other.push_back(productB); 
    } 

    printProducts(other); 
}