Маленький калькулятор

# include <iostream.h>
# include <iomanip.h>
# include <math.h>
 int main()
 {
  int a,b,c,d;
///////////////////////////////////////////////////
/////////////Начало окна приветствия///////////////
///////////////////////////////////////////////////
  cout<<"===================="<<endl;
  cout<<"Welcome to 'Simple Calc' By_Dioxis"<<endl;
  cout<<"===================="<<endl;
  cout<<"Please make your choice: "<<endl;
  cout<<" --------- "<<endl;
  cout<<"1 - Addition"<<endl
  <<"2 - Subtraction"<<endl
  <<"3 - Multiplication"<<endl
  <<"4 - Division"<<endl
  <<"5 - Erection of degree(stepen)"<<endl
  <<"6 - Radical of First number"<<endl
  <<"7 - Pifagor square"<<endl;
  cout<<"___________________"<<endl;
  cin>>c;  
///////////////////////////////////////////////////
////Окончание окна приветствия - пошла выборка/////
///////////////////////////////////////////////////
  if ( c < 5 ) //Проверяем условие
  {
  cout<<"Enter First number Plz:"<<endl;
  cin>>a;
  cout<<"Enter Second number(degree) Plz:"<<endl;
  cin>>b;
  switch(c) //Выбор
  {  
  case 1 :
  d = a+b;
  break;
  case 2 :
  d = a-b;
  break;
  case 3 :
  d = a*b;
  break;
  case 4 :
  d = a/b;
  break;
  } //Окончание выбора
  cout<<"===================="<<endl;
  cout<<"Your Answer will be: "<<d<<endl;
  cout<<"===================="<<endl;
  }
///////////////////////////////////////////////////
//////////////////Пошли условия////////////////////
///////////////////////////////////////////////////
 
  if ( c = 5 ) //Усли условие верно 1
  {
  cout<<"Enter Your Number Plz:"<<endl;
  cin>>a;
  cout<<"Enter Your Degree (Stepen') Plz:"<<endl;
  cin>>b;
  d=pow(a,b);
  cout<<"===================="<<endl;
  cout<<"Your Answer will be: "<<d<<endl;
  cout<<"===================="<<endl;
  }
  if ( c = 6 ) //Если условие верно 2
  {
  cout<<"Enter Your Number Plz:"<<endl;
  cin>>a;
  d=sqrt(a);
  cout<<"===================="<<endl;
  cout<<"Your Answer will be: "<<d<<endl;
  cout<<"===================="<<endl;
  }
  if ( c = 7 ) //Если условие верно 3
  {
  cout<<"===================="<<endl;
  cout<<"Pifagor square:"<<endl;
  cout<<"===================="<<endl;
  for(int i=1; i<=9; i++) {
  for(int j=1; j<=9; j++)
  cout << setw(3) << i*j;
  cout << endl;
  }}
  
  else //Если условие неверно
  {
  cout<<"===================="<<endl;
  cout<<"Enter Valid number Plz!"<<endl;
  cout<<"===================="<<endl;
  }
return 0;
}