Vector - C++

Program:

#include<iostream>
using namespace std;
class vector
 {
   int a[20],i,j,k,n,s,p;
   public:
    void creat();
    void modify();
    void mult();
    void display();
  };
  void vector::creat()
   {
     cout<<"\nEnter number of elements:";
     cin>>n;
     cout<<"\nEnter elements:";
     for(i=1;i<=n;++i)
      cin>>a[i];
    }
   void vector::display()
    {
      cout<<"\nVector is:";
      for(i=1;i<=n;++i)
       cout<<a[i]<<"\t";
     }
    void vector::mult()
     {
      cout<<"\nEnter the scalar to be multiplied:";
      cin>>s;
      for(i=1;i<=n;++i)
       a[i]=a[i]*s;
      cout<<"\nVector after multiplication";
        display();
      }
      void vector::modify()
      {
        cout<<"\nEnter no. to be inserted:";
        cin>>j;
        cout<<"\n Enter position to insert:";
        cin>>p;
        for(i=n;i>=p;--i)
        
           a[i+1]=a[i];
           a[i+1]=j;
           n++;
       }
        int main()
       {
         vector ob1;
         int ch,k=1;
         while(k==1)
         {
          cout<<"\nMENU\n\n1.TO CREATE VECTOR\n2.TO DISPLAY\n3.TO MULTIPLY BY A SCALAR\n4.TO INSERT TO A POSITION\n5.EXIT\nENTER YOUR CHOICE";
          cin>>ch;
          switch(ch)
             {
                 case 1:ob1.creat();
                        break;
                  case 2:ob1.display();
                         break;
                  case 3: ob1.mult();
                          break;
                   case 4:ob1.modify();
                          break;
                    case 5:k=0;
                           break;
                }
             }
             return 0;
          }