C++程序为什么我类里的SET（）函数中的赋值运算无法执行

#include<iostream>
#include<string>
using namespace std;
int joblength; int jobname;int i;int j;
class usedtable
{public:
 int adress[5];
 int length[5];
 int taskname[5];
public:  
  void set();
 };
usedtable used_table;

void usedtable::set()
{ used_table.adress[0]=0;
  used_table.adress[1]=5;
  used_table.adress[2]=10;
  used_table.adress[3]=15;
  used_table.adress[4]=20;
  used_table.length[0]=5;
  used_table.length[1]=5;
  used_table.length[2]=5;
  used_table.length[3]=5;
  used_table.length[4]=5;
  used_table.taskname[0]=0;
  used_table.taskname[1]=0;
  used_table.taskname[2]=0;
  used_table.taskname[3]=0;
  used_table.taskname[4]=0;
  cout<<"usedtable"<<endl;
  for(i=0;i<5;i++)
{cout<<used_table.adress[i]<<'\t'<<used_table.length[i]<<'\t'<<used_table.taskname[i]<<'\t'<<endl;}

}




class freetable
{public:
 int adress1[5];
 int length1[5];
 int flag[5];
public:
  void set();
  };

freetable free_table;
void freetable::set()
{ free_table.adress1[0]=25;
  free_table.adress1[1]=30;
  free_table.adress1[2]=35;
  free_table.adress1[3]=40;
  free_table.adress1[4]=45;
  free_table.length1[0]=5;
  free_table.length1[1]=5;
  free_table.length1[2]=5;
  free_table.length1[3]=5;
  free_table.length1[4]=5;
  free_table.flag[0]=0;
  free_table.flag[1]=0;
  free_table.flag[2]=0;
  free_table.flag[3]=0;
  free_table.flag[4]=0;
  cout<<"freetable"<<endl;
  for(i=0;i<5;i++)
  {cout<<free_table.adress1[i]<<'\t'<<free_table.length1[i]<<'\t'<<free_table.flag[i]<<'\t'<<endl;}
   
}




void main()
{ void usedtable::set();
  void freetable::set();
  cout<<"请输入作业长度"<<endl;
  cin>>joblength;
  cout<<"请输入作业名字"<<endl;
  cin>>jobname;
  for(j=0;j<5;j++)
{
if(used_table.taskname[j]=0&&used_table.length[j]>joblength)
{ used_table.taskname[j]=jobname;
  used_table.length[j]=joblength;
used_table.adress[j+1]=used_table.adress[j]+joblength;
used_table.length[j+1]+=used_table.length[j]-joblength;
   
}
  break;  
}
  cout<<"FREETABLE"<<endl;
  for(i=0;i<5;i++)
  { cout<<free_table.adress1[i]<<'\t'<<free_table.length1[i]<<'\t'<<free_table.flag[i]<<'\t'<<endl;}
  cout<<"UDESTABLE"<<endl;
  for(i=0;i<5;i++)
  {cout<<used_table.adress[i]<<'\t'<<used_table.length[i]<<'\t'<<used_table.taskname[i]<<'\t'<<endl;}
   
  cout<<"回收作业名字";
  cin>>jobname;
 for(j=0;j<5;j++)
  { if(used_table.taskname[j]=jobname)
  { used_table.taskname[j]=0;
  for(i=0;i<5;i++)
{if(free_table.length1[i]=used_table.length[j])
{ free_table.adress1[i]=used_table.adress[j];
  free_table.flag[i]=1;}
  if(free_table.length1[i]>used_table.length[j])
{ free_table.length1[i+1]+=free_table.length1[i]-used_table.length[j];
  free_table.adress1[j+1]=free_table.adress1[i]+used_table.length[j];
  free_table.length1[i]=used_table.length[j];
  free_table.flag[i]=1;}
break;}
  }
  break;}  
 cout<<"freetable";
 for(i=0;i<5;i++)
{cout<<free_table.adress1[i]<<'\t'<<free_table.length1[i]<<'\t'<<free_table.flag[i]<<'\t'<<endl;}
  cout<<"usedtable";  
 for(i=0;i<5;i++)
{cout<<used_table.adress[i]<<'\t'<<used_table.length[i]<<'\t'<<used_table.taskname[i]<<'\t'<<endl;}
 }

既然改的是全局变量的值，就没必要在成员函数里做这个了