#include <iostream>
using namespace std;
int main()
{
    int k,r,a,b,c,base,hight,;
    float area;
    
    cout<<"----------------------------------------"<<endl;
    cout<<"         "<<"MENU"<<endl;
    cout<<"     "<<endl;
    cout<<"    "<<"1. CIRCLE"<<endl;  
    cout<<"    "<<"2. RECTANGULER"<<endl;
    cout<<"    "<<"3. SQUARE"<<endl;
    cout<<"    "<<"4. TCIANGLE"<<endl;
    cout<<"---------------------------------------"<<endl;
    cout<<"k = ";
    cin>>k;
    
       if(k>0 && k<5)
          {
              if(k<3)
               {
                   if(k == 1)
                   {
                     cout<<"r=";  
                     cin>>r;
                     area = 3.1414*r*r;
                     cout<<"AREA ="<<area<<endl;
                   }
                   if(k == 2)
                   {
                     cout<<"a=";
                     cin>>a;
                     cout<<"b=";  
                     cin>>b;  
                     area = a*b;
                     cout<<"AREA ="<<area<<endl;
                   }    
               }
              else
                {
                   if(k == 3)
                   {
                      cout<<"c=";  
                      cin>>c;  
                     area = c*c;
                     cout<<"AREA ="<<area<<endl;
                   }
                   if(k == 4)
                   {
                     cout<<"base=";
                      cin>>base;
                     cout<<"hight=";    
                     cin>>hight;  
                     area = 0.5*base*hight;
                     cout<<"AREA = "<<area<<endl;
                   }    
                }        
          }
                    
      system("pause");
    return 0;
}
  

คือ เวลา run แล้วอยากให้มัน วนกลับไปถามใหม่ว่า ต้องการคิด อันไหน อีก ต้องเขียน ยังไงอ่าคะ แล้วถ้าจะให้ดี เคลียของเก่าด้วยก้อดี ^^ ขอบคุณค่าาา