C++ 程序菜单混乱

Question

In this C++ program, I keep getting an error that says "editor placeholder in source file" for case 'fa': findArea. I do not know what the problem is. I have tried to change it up to another name but haven't succeeded.

int main () 
{ 
 void findArea(double);
 void quit();
 void printHelp();

 case 'h':
 case 'H': printHelp(); //help text.
 break;

 case 'q':
 case 'Q': quit();  //quit program.
 break;

 case 'fa':
 case 'FA': findArea(); //find area of rectangle.
 break;
 }
 void quit(){ // end program
 cout << "Ending!"  << endl;
 }
 void printHelp(){ // help text

 cout << "Supported commands: \n"
       << "fa. find area./n"
       << "h. print help./n"
       << "q. quit./n"    
   }
 void findArea(){
  area = length * width;
 }

Answer 1

1. You have

 void findArea(double);
 void quit();
 void printHelp();

inside of your main function. Normally these would be outside of any function.

2. void findArea(double); is declared, but case 'FA': findArea(); is used and void findArea(){} is defined. Change:

void findArea(double);

to

void findArea();

Answer 2

Try this code .
Prob your code had :
You had function declaration in main() which is not allowed. There was one more mistake you had argument type double in area but in function body of area it was void so it is a argument mismatch compiler error.
Also your code has case statement without switch(). there are lot more errors like you had not declared variables not even taking input.

   #include<iostream>
   using namespace std;
  void findArea();
  void printHelp();
  void quit();
  int main ()
  { 
      char ch; 
      cout<<"Enter choice \n";
      cout<<"h for Help \n";
     cout<<"q for Quit \n"; 
    cout<<"fa to find area \n"; 
     cin>>ch;
      switch (ch)
      {
     case 'h':
    case 'H': printHelp(); //help text. 
                    break;
      case 'q':
       case 'Q': quit(); //quit program.
                      break; 
      case 'f':  
      case 'F':       findArea(); 
                           break;
      } 
 return 0;
  }
  void quit()
  { 
    cout << "Ending!" << endl;
  }  
   void printHelp()
   {
  // help text
 cout << "Supported commands: \n"; 
  cout<< "f. find area.\n" ;
 cout<< "h. print help.\n" ;
 cout<< "q. quit./n" ;
  } 
  void findArea()
  { 
   double l,w,area;
   cout<<"Enter Length \n";     
   cin>>l;
   cout<<"Enter Width \n";
   cin>>b;

   area = l * w; 
   cout<<"\n\tArea = "<<area;
   }