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Class Error

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Join Date: Mar 2007
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nayrb nayrb is offline Offline
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Class Error

 
0
  #1
Mar 4th, 2007
Hello,
I am having problems with reading from a .h file to .cpp file it gives me a strange error i have gone over this thing 1000 times and can not figure out whats wrong. Could someone please help me? I am using dev.c++ compiler. I should mention i am new at this class thing:cheesy:

ERROR
2 C:\Documents and Settings\MACHINE\Desktop\DAVID\w.cpp In file included from C:\Documents and Settings\MACHINE\Desktop\DAVID\w.cpp

THIS IS THE .H FILE

C++ Syntax (Toggle Plain Text) 
  1.  
  2. // FILE w.h
  3.  
  4.  
  5. #ifndef SHIP_STATE
  6. #define SHIP_STATE
  7.  
  8. class ship_state 
  9. {
  10. public:
  11.  
  12.    ship_state(double h, double v, double f);
  13.    double height();
  14.    double velocity();
  15.    double fuel();
  16.    int landed();
  17.    ship_state& update(double rate);
  18.    void print(ostream& os);
  19.    double dt  const;
  20.    double gravity const;
  21.    double engine_strength const;
  22.    double safe_velocity const;
  23.    char burn_key const;
  24. private:
  25.    double height_;
  26.    double velocity_;
  27.    double fuel_;
  28. };
  29.  
  30. #endif
  31.  
  32. THIS IS THE .CPP FILE
  33.  
  34.  
  35. #include "w.h"
  36. #include <iostream>
  37. using namespace std;
  38.  
  39. ship_state::ship_state(double h, double v, double f)
  40. {
  41.    height_ = h;
  42.    velocity_ = v;
  43.    fuel_ = f;
  44. }
  45.  
  46. double ship_state::height() {return height_;}
  47. double ship_state::velocity(){return velocity_;}
  48. double ship_state::fuel() {return fuel_;}
  49.  
  50. int ship_state::landed()
  51. {
  52.    if (height_<=0)
  53.       return 1;
  54.    return 0;
  55. }
  56.  
  57. void ship_state:print(ostream& os)
  58. {
  59.    os<<"Velocity :"<<velocity_<<endl;
  60.    os<<"Height   :"<<height_<<endl;
  61.    os<<"Fuel     :"<<fuel_<<endl;
  62. }
  63.  
  64. ship_state& ship_state::update(double rate)
  65. {
  66.    double dh;
  67.    double dv;
  68.    if (fuel_<=0) {
  69.       fuel_=0;
  70.       rate=0;
  71.    }
  72.    dh=velocity_*dt;
  73.    dv=engine_strength*rate-gravity;
  74.    fuel_ -= (rate*dt);
  75.    height_ += dh;
  76.    velocity_+=dv;
  77.    return *this;
  78. }
  79. void end_game(ship_state&s);
  80. double get_burn_rate();
  81.  
  82. void lander_loop(ship_state& s)
  83. {
  84.    s.print(cout);
  85.    if (s.landed())
  86.       end_game(s);
  87.    else
  88.       lander_loop(s.update(get_burn_rate()));
  89. }
  90.  
  91. void end_game(ship_state& s)
  92. {
  93.    double v=s.velocity();
  94.    cout<<"Final velocity: "<<v;
  95.    if (v>=safe_velocity)
  96.       cout<<"...good landing!\n";
  97.    else
  98.       cout<<"...you crashed!\n";
  99. }
  100.  
  101. double get_burn_rate()
  102. {
  103.    cout<<"Enter "<<burn_key<<" to burn fuel, any other to float :";
  104.    char ch;
  105.    cin>>ch;
  106.    if (ch==burn_key)
  107.       return 1.0;
  108.    else
  109.       return 0.0;
  110. }
  111.    double dt=1.0  const;
  112.    double gravity=0.5  const;
  113.    double engine_strength=1.0 const;
  114.    double safe_velocity = -0.5 const;
  115.    char burn_key='b'const;
Last edited by nayrb; Mar 4th, 2007 at 3:25 pm.
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Re: Class Error

 
0
  #2
Mar 4th, 2007
The way you are trying to incorporate the wrong concept of const variables in your program is causing all the problems.

If you declare a variable as const, you need to specify the const qualifier before the dataype, like this:

c Syntax (Toggle Plain Text) 
  1. const int SIZE = 10 ; // you must specify the value

Since const variables can't be modified (alteast not using the same name) you need to specify an initial value for the variable the way I have done above. Also since initialization of non static members inside a class is not allowed in C++, so you have to make those variables static.

C++ Syntax (Toggle Plain Text) 
  1.    static const double dt=1.0  ;
  2.    static const double gravity=0.5 ;
  3.    static const double engine_strength = 1.0 ;
  4.    static const double safe_velocity = -0.5 ;
  5.    static const char burn_key = 'b';

You could also create a seperate header file with the constants and include it whenever you need to use the values.
I don't accept change; I don't deserve to live.
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Re: Class Error

 
0
  #3
Mar 4th, 2007
Oh. DAA. I feel like a retard. Thanks. Did not know about the whole static thing. That response was quick.
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