C++ 中的矩阵向量乘法

Question

我有一个矩阵和向量相乘的代码。但是，它不会 进入友元函数 for

 中的 

calc()

循环内部。你能发现错误吗？

#include<iostream>
using namespace std;

class vector;
class matrix
{
public:
    int r,c,ma[10][10];
    void get(int r, int c=3)
    {
        int i,j;
        cout<<"Enter the matrix elements\n";
        for(i=0; i<r; i++)
            for(j=0; j<c; j++)
            {
                cin>>ma[i][j];
            }
        cout<<"Your input: ";
        for(i=0; i<r; i++)
        {
            cout<<"\n";
            for(j=0; j<c; j++)
            {
                cout<<ma[i][j]<<"\t";
            }
        }
    }
    friend void calc(matrix m,vector v);
};

class vector
{
public:
    int val,va[10];
    void get(int v=3)
    {
        int i;
        cout<<"\nEnter the vector values\n";
        for(i=0; i<v; i++)
        {
            cin>>va[i];
        }
        cout<<"\nYour input:\n";
        for(i=0; i<v; i++)
        {
            cout<<va[i]<<"\t";
        }
    }
    friend void calc(matrix m,vector v);
};

void calc(matrix m,vector v)
{
    int c[10],i,j;
    if(m.c == v.val)
    {
        for(i=0; i<v.val; i++)
        {
            cout<<"Entered 1st loop";
            c[i] = 0;
            for(j=0; j<m.r; j++)
            {
                c[i] = c[i]+(m.ma[i][j] * v.va[j]);
            }
        }
    }
    cout<<"\nThe result is :\n";
    for(i=0; i<m.r; i++)
    {
        cout<<"Entered for";
        cout<<"\n"<<c[i];
    }
}

int main()
{
    int r;
    matrix m1;
    vector v1;
    cout<<"Enter the number of rows = ";
    cin>>r;
    m1.get(r);
    v1.get();
    calc(m1,v1);
    return 0;
}

Answer 1

您永远不会在

val

类中初始化

vector

，也不会在

r

类中初始化

c

和

matrix

。因此，检查

if(m.c == v.val)

永远无法通过，因为这些成员的值是 未定义（包含随机垃圾）。

我建议您看一下 The Definitive C++ Book Guide and List；一本好书将帮助您掌握基础知识。

Answer 2

#include<iostream>
#include<math.h>
#include<windows.h>

using namespace std;

class vecter;
class matrix
{
    int matrex[3][3];
public:
    
    friend void multiply(matrix &,vecter &);
    void setmatrix()
    {
       cout<<"Enter the elements into the matrix array "<<endl;
        for(int i=0;i<3;i++)
            {
                for(int j=0;j<3;j++)
                {
                    cout<<"Enter the element in to the "<<i+1<<" row and "<<j+1<<" column "<<endl;
                    cin>>matrex[i][j];
                }
            }
    }
    void dismatrix()
    {
       cout<<" The elements into the matrix array are "<<endl;
        for(int i=0;i<3;i++)
            {
                cout<<"|";
                for(int j=0;j<3;j++)
                {
                    cout<<":"<<matrex[i][j]<<" : ";
                }
                cout<<"|";
                cout<<endl;
            }
    }
};
class vecter
{
    int vector[3];
public:
    
    friend void multiply(matrix &,vecter &);
    void setvector()
    {
        for(int i=0;i<3;i++)
        {   cout<<"Enter the "<<i+1<<" element in to the vector Array "<<endl;
            cin>>vector[i];
        }
    }

    void disvector()
    {
        cout<<"The elements in the index of the vector array are "<<endl;
        for (int i=0;i<3;i++)
        {
            cout<<"|"<<vector[i]<<"|"<<endl;
        }
    
    }
};
void multiply (matrix &m,vecter &v)
{
    int solution[3];
    //initilization.
    for(int i=0;i<3;i++)
    {
        solution[i]=0;
    }
    //multiplication.
    for(int i=0;i<3;i++)
    {
        for(int j=0;j<3;j++)
        {
            
             solution[i]+=( m.matrex[i][j]*v.vector[j]);
        }
    
    }
    cout<<"\t\t\t\t\t processing..... ";
        for(int i=0;i<20;i++)
        {
            cout<<char(219);
            Sleep(200);    
        }
        cout<<endl;
        for(int i=0;i<3;i++)
        {
            cout<<"|"<<solution[i]<<"|"<<endl;
        }

}
int main()
{
    matrix m;
    vecter v;
    v.setvector();
    m.setmatrix();
    m.dismatrix();
    cout<<endl;
    v.disvector();
    multiply(m,v);
    system ("pause>0");

}