f0815.cpp

it is a usefull thing

//=====================================
// f0815.cpp
// normal function accessing class member
//=====================================
#include<iostream>
#include<fstream>
using namespace std;
//-------------------------------------
class Vector{
  int* v;             //指向一个数组,表示向量
  int sz;
public:
  void remove(){ delete[] v; }
  int size(){ return sz; }
  void set(int);
  void display();
  int& operator[](int);
};//-----------------------------------
void Vector::set(int s){
  sz = s;
  if(s<=0){
    cerr<<"bad Vector size.\n";
    exit(1);
  }
  v = new int[s];
}//------------------------------------
int& Vector::operator[](int i){          //引用返回的目的是返回值可以作左值
  if(i<0 || i>=sz){
    cerr <<"Vector index out of range.\n";
    exit(1);
  }
  return v[i];
}//------------------------------------
void Vector::display(){
  for(int i=0; i<sz; ++i)
    cout<<v[i]<<" ";
  cout<<"\n";
}//------------------------------------
class Matrix{
  int* m;
  int szl, szr;
public:
  void set(int, int);
  void remove(){ delete[] m; }
  int sizeL(){ return szl; }
  int sizeR(){ return szr; }
  int& elem(int, int);
};//-----------------------------------
void Matrix::set(int i, int j){
  szl = i; szr = j;
  if(i<=0 || j<=0){
    cerr <<"bad Matrix size.\n";
    exit(1);
  }
  m = new int[i*j];
}//------------------------------------
int& Matrix::elem(int i, int j){      //引用返回的目的是返回值可以作左值
  if(i<0||szl<=i||j<0||szr<=j){
    cerr <<"Matrix index out of range.\n";
    exit(1);
  }
  return m[i*szr+j];
}//------------------------------------
Vector multiply(Matrix& m, Vector& v){  //矩阵乘向量
  if(m.sizeR()!=v.size()){
    cerr <<"bad multiply Matrix with Vector.\n";
    exit(1);
  }
  Vector r;
  r.set(m.sizeL());       //创建一个存放结果的空向量
  for(int i=0; i<m.sizeL(); i++){
    r[i] = 0;
    for(int j=0; j<m.sizeR(); j++)
      r[i] += m.elem(i,j) * v[j];
  }
  return r;
}//------------------------------------
int main(){
  ifstream in("in.txt");
  int x,y;  in>>x>>y;
  Matrix ma;
  ma.set(x,y);
  for(int i=0; i<x; ++i)
  for(int j=0; j<y; ++j)
    in>>ma.elem(i,j);
  in>>x;
  Vector ve;
  ve.set(x);
  for(int i=0; i<x; ++i)
    in>>ve[i];
  Vector vx = multiply(ma,ve);
  vx.display();
  ma.remove();
  ve.remove();
  vx.remove();
}//====================================