c++ - 当用户从命令行给出浮点数时，为什么我的 C++ 程序一直冻结？

Question

我正在用 c++ 编写一个程序，它将找到幂集的总和。我想包括一些错误处理来清除诸如 0、字符或非整数之类的东西。我的策略很简单。程序进入一个无限while循环，只有当用户输入的模数为零时才能退出。我期望发生的事情：用户输入 2.4 (2.4 % 1 = .4, .4 != 0) 程序再次循环并告诉用户输入一个整数。会发生什么：用户进入 2.4，程序冻结。

有人可以告诉我发生了什么事吗？

谢谢

// This C++ program will compute sum of all subsets of a set "S" stored 
// in an array data structure.  We assume that these subsets are the 
// powerset of S and not the permutation set.  
// The program workflow is as follows:
//
// 1)   Prompt the user to provide the length and elemets to a custom array, if none, use 
//      the default array.
// 2)   The user creates a custom array.
// 3)   Sort the array using the QuickSort function.
// 4)   Get the sum by running the SubArraySum function

#include<iostream>
#include<limits>
#include<cmath>
using namespace std; 

// Utility functions for quicksort
void Swap(int *x, int *y)
{
    int temp = *x;
    *x = *y;
    *y = temp;
}

int RemoveDuplicates(int arr[], int size)
// This function removes duplicate elements by setting their value to 
// zero.  This works because the purpose of the main code is to sum the subarrays.
// Adding zero to the sum multiple times does not change the sum.  However, technically this will
// shorten the array.  
// So, we need to keep track of the number of duplicates and give this to the SubArraySum
// function since it used the length of the array to calculate the sum.   
{
    int dupCount = 0;
    for(int i = 0; i < size-1; i++)
    {
        if(arr[i] == 0)
        {
            ;
        }
        if(arr[i] == arr[i+1])
        {
            arr[i] = 0;
            dupCount++;
        }
    }

    return dupCount;
}

int Partition(int arr[], int low, int high)
{
    int i = low - 1;
    int pivot = arr[high];

    for(int j = low; j <= high - 1; j++)
    {
        if(arr[j] < pivot)
        {
            i++;
            Swap(&arr[i], &arr[j]);
        }
    }
    Swap(&arr[i+1], &arr[high]);

    return i+1;
}

void PrintArray(int arr[], int size)
{
    cout << "[ ";
    for(int i = 0; i < size-1; i++)
    {
        cout << arr[i] << ", ";
    }
    cout << arr[size-1] << " ]" << endl;
}

// Quicksort to sort the array
void QuickSort(int arr[], int low, int high)
{
    if(low < high)
    {
        int p_idx = Partition(arr, low, high); // p_idx is the partition index
        QuickSort(arr, low, p_idx-1);
        QuickSort(arr, p_idx+1, high);
        
    }
}


void GetSum(int arr[], int n, int dupCount) 
// Computes sum all sub-array 
// arr[] is an array provided by the user or if none given the 
// default array is arr[] = {1,2,3,4...10}
{ 
    int p = pow(2, n-1-dupCount);
    long int sum = 0; 

    //cout << "These are the subarrays: " << endl;
    // The outer forloop picks the starting point for each subarray
    for (int i=0; i < n; i++) 
    { 
        sum += p*arr[i];        
    } 
    cout << "This is the sum: " << sum << endl; 
} 

void SubArraySum(int arr[], int size)
{
    PrintArray(arr, size);  
    QuickSort(arr, 0, size-1);
    int dupCount = RemoveDuplicates(arr, size);     
    GetSum(arr, size, dupCount);
}

void DefaultSubArraySum()
{
    int arr[] = {1,2,3,4,5,6,7,8,9,10};
    int n = sizeof(arr)/sizeof(arr[0]); 
    SubArraySum(arr, n);
}


// Driver program to test above function 
int main() 
{   
    cout << "Enter a whole number for the length of the array or enter 0: ";    
    
    // This while loop will chatch any entries that were not whole numbers and force 
    // the user into a loop until they give a valide number.
    
    double user_length;
    cin >> user_length;
    while(1)
    {
        double is_whole = fmod(user_length,1.0);


        if(cin.fail())
        {
            cin.clear();
            cin.ignore(numeric_limits<streamsize>::max(),'\n');
            cout << "Entry invalid.  Please enter a whole number or enter 0: ";
            cin >> user_length;
        }

        if(is_whole != 0.0)
        {
            cin.clear();
            cin.ignore(numeric_limits<streamsize>::max(),'\n');
            cout << "Entry invalid.  Please enter a whole number or enter 0: ";
            cin >> user_length;
        }

        

        if(is_whole == 0.0)
        {
            break;
        }

    }
        
    // If the user does not specify an array the default sub array sum will be calculated.  
    if(user_length == 0.0)
    {
        // Default code if the user enters 0.
        DefaultSubArraySum();

    }
    else
    {
        cout << "this user_length: " << user_length << endl;
        int arr[(int)user_length];
        cout << "Enter your array values: "  << endl;
        for(int i = 0; i < user_length; i++)
        {
            cout << i+1 << ": ";
            cin >> arr[i];
            
        }       

        int n = sizeof(arr)/sizeof(arr[0]); 
        SubArraySum(arr, n);
        
    }
        
    
    int clear_buffer = cin.get();
    return 0; 
} 

标签： c++command-line-interface

Answer 1

好的，所以问题是我使用 % 作为我的模数运算符。这是一个二元运算符，当我使用变量 int user_length 运行它时它失败了。为了解决这个问题，我删除#include<math.h>并添加了#include <cmath>. 我删除了 % 运算符并将其替换为 fmod(x,y) 函数。这纠正了冻结问题。但是，代码仍在与字符作斗争。出于某种奇怪的原因，如果一个字符连续输入两次，is_whole 将变为 0，并且我的默认函数将运行。向@churill 大声疾呼，因为他发现了 % mod 冲突。

这是一个简化的，主要是工作代码。

#include<iostream>
#include<limits>
#include<cmath>
using namespace std; 

void PrintArray(int arr[], int size)
{
    cout << "[ ";
    for(int i = 0; i < size-1; i++)
    {
        cout << arr[i] << ", ";
    }
    cout << arr[size-1] << " ]" << endl;
}


// Driver program to test above function 
int main() 
{   
    cout << "Enter a whole number for the length of the array or enter 0: ";    
    
    // This while loop will chatch any entries that were not whole numbers and force 
    // the user into a loop until they give a valide number.
    
    double user_length;
    cin >> user_length;
    while(1)
    {
        double is_whole = fmod(user_length, 1.0);
        cout << "This is the value of is_whole: " << is_whole << endl;


        if(cin.fail())
        {
            cin.clear();
            cin.ignore(numeric_limits<streamsize>::max(),'\n');
            cout << "Entry invalid.  Please enter a whole number or enter 0: ";
            cin >> user_length;
        }
        
        if(is_whole != 0.0)
        {
            cin.clear();
            cin.ignore(numeric_limits<streamsize>::max(),'\n');
            cout << "Entry invalid.  Please enter a whole number or enter 0: ";
            user_length = 0;
            cin >> user_length;
        }       

        if(is_whole == 0.0)
        {
            break;
        }

    }
        
    // If the user does not specify an array the default sub array sum will be calculated.  
    if(user_length == 0.0)
    {
        // Default code if the user enters 0.
        cout << "The user entered 0 " << endl;

    }
    else
    {
        cout << "this user_length: " << user_length << endl;
        int arr[(int)user_length];
        cout << "Enter your array values: "  << endl;
        for(int i = 0; i < user_length; i++)
        {
            cout << i+1 << ": ";
            cin >> arr[i];
            
        }       

        int n = sizeof(arr)/sizeof(arr[0]); 
        PrintArray(arr, n);
        
    }
        
    
    int clear_buffer = cin.get();
    return 0; 
}