外部元素的总和 - 函数 C++ 的矩阵

Question

我需要创建一个计算矩阵外部元素的程序。矩阵应由用户设置。 我的想法是创建程序的第一部分，用户可以在其中编写矩阵的元素，然后将该矩阵提供给将内部元素设置为 0 的函数，然后将其返回给 main() 然后启动另一个计算所有元素总和的函数。 问题是我无法将在主 {} 中声明的矩阵传递给函数。 我几乎可以肯定我需要使用指针，但是我不知道在这种情况下如何使用它们......你能帮忙吗？ 这就是我目前写的代码：

 #include <iostream>
#define MAX 10
using namespace std;
int zeroMatrix (int mat [][10], int, int);
int main()
{   //ask the user the number of rows and columns of the matrix.
    int rows,cols;
    cout << "please insert the number of rows: ";
    cin >> rows;
    cout << "insert the number of columns: ";
    cin >> cols;
    //accepting values
    int matrix [rows] [cols];
    for (int i=0; i<rows; i++)
        {
        for (int j=0; j<cols; j++)
            {
                cout <<"insert the element A(" << i <<","<< j << ") of the matrix " ;
                cin >> matrix[i][j];
            }
        }
    zeroMatrix (matrix [rows][cols]);
}

//change the previous matrix into a new matrix with the internal elements = 0

 int zeroMatrix (int mat [][10], int rows, int cols )
 {
    for (int i=1; i<rows-1; i++)
        { for (int j=1; j<cols-1 ; j++)
            {
                mat[i][j] = 0;
            }
        }
 }

Answer 1

    #include <iostream>

    using namespace std;

    void zeroMatrix (int **mat, int, int);//makes the inner elements zero

    int sumExternals(int **mat, int rows, int cols);//sums the external elements without
                                               //using  zeroMatrix

    void printMatrix(int **mat, int, int);//prints a matrix on the console window

    int main()
    {   //ask the user the number of rows and columns of the matrix.
        int rows,cols;
        cout << "please insert the number of rows: ";
        cin >> rows;
        cout << "insert the number of columns: ";
        cin >> cols;
        //accepting values

        int **matrix = new int*[rows];

        for(int i=0; i<rows; ++i)
           matrix[i] = new int[cols];

        for (int i=0; i<rows; i++)
            {
            for (int j=0; j<cols; j++)
                {
                    cout <<"insert the element A(" << i <<","<< j << ") of the matrix " ;
                    cin >> matrix[i][j];
                }
            }

        printMatrix(matrix,rows,cols);          //print the matrix
        cout<<sumExternals(matrix,rows,cols)<<endl;  //get the sum of the external elements

        //Just so you can see how to proper call the function zeroMatrix
        zeroMatrix(matrix,rows,cols);
        printMatrix(matrix,rows,cols);
    }

    //changes the previous matrix into a new matrix with the internal elements = 0
    void zeroMatrix (int **mat, int rows, int cols )
     {
        for (int i=1; i<rows-1; i++)
             for (int j=1; j<cols-1; j++)
                mat[i][j] = 0;


     }

    //calculates the sum of the external elements of a matrix
    int sumExternals(int **mat, int rows, int cols)
    {
        int sum = 0;
        for(int j=0;j<cols;++j)
        {
            sum+=mat[0][j];         // adds the upper bound elements to sum
            sum+=mat[rows-1][j];    // adds the lower bound elements to sum
        }

        //Take caution not to add elements which are already taken into account
        for(int i=1;i<rows-1;++i)
        {
            sum+=mat[i][0];         //adds the left bound elements to sum
            sum+=mat[i][cols-1];    //adds the right bound elements to sum

        }

        return sum;
    }

    void printMatrix(int **matrix, int rows, int cols)
    {
        for(int i=0;i<rows;++i)
        {
            for(int j=0;j<cols;++j)
                cout<<matrix[i][j]<<" ";

            cout<<endl;
        }
   }

我添加了函数 sumExternals，它计算外部矩阵元素的总和，但没有使用您的 zeroMatrix 函数。

Answer 2

使用 vector 代替数组。此外，不需要两个单独的功能。一种是求外部元素之和，另一种是将内部元素设置为 0。您可以在同一个功能中实现这两项任务。请参阅下面编写的函数 external_elements_sum。

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

int external_elements_sum(vector<vector<int> >&arr)    // function that finds sum of external elements and set internal elements to 0
{
    int sum=0;
    for(int i=0; arr.size()>0 && i<arr[i].size();i++)
    {
        for(int j=0;j<arr[i].size();j++)
        {
            if(i==0 || i==arr.size()-1 || j==0 || j==arr[i].size()-1)  // external elements
                sum+=arr[i][j];
            else arr[i][j]=0;     // internal elements
        }
    }
    return sum;
}

int main() {
    vector< vector<int> >arr;
    int i,j,number,rows=3,cols=4;
    for(i=0;i<rows;i++)
    {
        vector<int>v;
        for(j=0;j<cols;j++)
        {
            cin>>number;
            v.push_back(number);
        }
        arr.push_back(v);
    }
    int sum = external_elements_sum(arr);
    for(i=0;i<arr.size()>0 && arr[0].size();i++)   // arr.size()>0 to check corner case like if row is 0
    {
        for(j=0;j<arr[i].size();j++)
            cout<<arr[i][j]<<" ";
        cout<<endl;
    }
    cout<<"Sum of externale elements is: "<<sum;
    return 0;
}

Input:
1 2 3 4
5 6 7 8
2 5 1 4

Output:
1 2 3 4 
5 0 0 8 
2 5 1 4 
Sum of externale elements is: 35