helpclass.cpp

一个很好很有一思念的帮助类 是用C++写成的

/*  
   Project 8-1  
  
   Convert the Help system from Project 3-3 into  
   a Help class. 
*/  
  
#include <iostream>  
using namespace std;  
 
// A class that encapsulates a help system.   
class Help { 
public: 
  void helpon(char what); 
  void showmenu(); 
  bool isvalid(char ch); 
}; 
 
// Display help information. 
void Help::helpon(char what) { 
  switch(what) {  
    case '1':  
      cout << "The if:\n\n";  
      cout << "if(condition) statement;\n";  
      cout << "else statement;\n";  
      break;  
    case '2':  
      cout << "The switch:\n\n";  
      cout << "switch(expression) {\n";  
      cout << "  case constant:\n";  
      cout << "    statement sequence\n";  
      cout << "    break;\n";  
      cout << "  // ...\n";  
      cout << "}\n";  
      break;  
    case '3':  
      cout << "The for:\n\n";  
      cout << "for(init; condition; iteration)";  
      cout << " statement;\n";  
      break;  
    case '4':  
      cout << "The while:\n\n";  
      cout << "while(condition) statement;\n";  
      break;  
    case '5':  
      cout << "The do-while:\n\n";  
      cout << "do {\n";  
      cout << "  statement;\n";  
      cout << "} while (condition);\n";  
      break;  
    case '6':  
      cout << "The break:\n\n";  
      cout << "break;\n";  
      break;  
    case '7':  
      cout << "The continue:\n\n";  
      cout << "continue;\n";  
      break;  
    case '8':  
      cout << "The goto:\n\n";  
      cout << "goto label;\n";  
      break;  
  }  
  cout << "\n";  
}  
 
// Show the help menu. 
void Help::showmenu() { 
  cout << "Help on:\n";  
  cout << "  1. if\n";  
  cout << "  2. switch\n";  
  cout << "  3. for\n";  
  cout << "  4. while\n";  
  cout << "  5. do-while\n";  
  cout << "  6. break\n";  
  cout << "  7. continue\n";  
  cout << "  8. goto\n";  
  cout << "Choose one (q to quit): ";  
} 
 
// Return true if a selection is valid. 
bool Help::isvalid(char ch) {  
  if(ch < '1' || ch > '8' && ch != 'q') 
    return false; 
  else 
    return true; 
} 
 
int main() 
{ 
  char choice; 
  Help hlpob; // create an instance of the Help class. 
   
  // Use the Help object to display information. 
  for(;;) { 
    do { 
      hlpob.showmenu(); 
      cin >> choice; 
    } while(!hlpob.isvalid(choice)); 
  
    if(choice == 'q') break; 
    cout << "\n"; 
 
    hlpob.helpon(choice); 
  } 
  
  return 0;  
}