Programming Forums > Application Development > C++

ARTillery · Oct 4th, 2005, 10:28 AM

Hi all,
I'm back again with another question

her's a program from the book I'm studying to learn C++ (C++ programming for the absolute beginner), in this program the programmer uses a while loop..from what I understand while tests a condition and if it's true, it continues to perform whatever it's supposed to do..

here in the example..the while doesn't test anything..the programmer just assigned a value to a variable..

(Toggle Plain Text)

//4.4 - The Snail Racing Game -Dirk Henkemans 
//and Mark Lee - Premier Press
#include <iostream>
#include <ctime>
using namespace std;

//function declarations
int main(void);
int race(int, int);
void race(void);
int menu(void);
int placeBet(int);
void ini(void);

//variables
int money = 200;

//the main function
int main(void)
{
     ini();

     int userResponse;
     cout<< "Welcome to the snail races!!!" <<endl;
     while(userResponse = menu())
     {
          switch(userResponse)
          {
          case 1:
          case 2:
          case 3:
               ::money += 
               race(placeBet(userResponse), userResponse);
               break;
          case 4: //the user did not bet
               race();
               break;
          }
     }
     return 0;
}

//displays the main menu and 
//returns the user�s selection
int menu(void)
{
     int UR;//userResponse;
     cout << "You have " << money << " dollars."<< endl;
     do
     {
          cout<< "Races Menu" <<endl
               << "1) Bet on snail 1" << endl
               << "2) Bet on snail 2" << endl
               << "3) Bet on snail 3" << endl
               << "4) Just Watch" << endl
               << "0) leave the races" << endl;
          cin>> UR;
     }
     while(UR < 0 && UR > 4); 
     return UR;
}

//decides how much a person will bet on the snail
int placeBet(int userResponse)
{
     int betAmount;
     cout<< "Snail " << userResponse << " is a good choice!"
          << endl;
     cout<< "How much would you like to bet on your snail "
          << userResponse <<"?";
     cin >> betAmount;
     return betAmount;
}
//if they are just watching the race
void race (void)
{
     race(0, 0);
}

//if they are betting money
int race (int money, int userResponse)
{
     //stores the random number
     int winner = rand() % 3 + 1;
     cout<< "And the snails are off" << endl
          << "Look at them GO!!!" << endl
          << "The winner is snail " << winner;
     if(winner == userResponse)
     {
          cout<< "You Win!" <<endl;
          return 2 * money;
     }
     cout<<"You loose " << money << " dollars." <<endl;
     return -1 * money;
}

//handles program initializations
void ini(void)
{
     srand(time(0));
}

//4.4 - The Snail Racing Game -Dirk Henkemans 
//and Mark Lee - Premier Press
#include <iostream>
#include <ctime>
using namespace std;

//function declarations
int main(void);
int race(int, int);
void race(void);
int menu(void);
int placeBet(int);
void ini(void);

//variables
int money = 200;

//the main function
int main(void)
{
     ini();

     int userResponse;
     cout<< "Welcome to the snail races!!!" <<endl;
     while(userResponse = menu())
     {
          switch(userResponse)
          {
          case 1:
          case 2:
          case 3:
               ::money += 
               race(placeBet(userResponse), userResponse);
               break;
          case 4: //the user did not bet
               race();
               break;
          }
     }
     return 0;
}

//displays the main menu and 
//returns the user�s selection
int menu(void)
{
     int UR;//userResponse;
     cout << "You have " << money << " dollars."<< endl;
     do
     {
          cout<< "Races Menu" <<endl
               << "1) Bet on snail 1" << endl
               << "2) Bet on snail 2" << endl
               << "3) Bet on snail 3" << endl
               << "4) Just Watch" << endl
               << "0) leave the races" << endl;
          cin>> UR;
     }
     while(UR < 0 && UR > 4); 
     return UR;
}

//decides how much a person will bet on the snail
int placeBet(int userResponse)
{
     int betAmount;
     cout<< "Snail " << userResponse << " is a good choice!"
          << endl;
     cout<< "How much would you like to bet on your snail "
          << userResponse <<"?";
     cin >> betAmount;
     return betAmount;
}
//if they are just watching the race
void race (void)
{
     race(0, 0);
}

//if they are betting money
int race (int money, int userResponse)
{
     //stores the random number
     int winner = rand() % 3 + 1;
     cout<< "And the snails are off" << endl
          << "Look at them GO!!!" << endl
          << "The winner is snail " << winner;
     if(winner == userResponse)
     {
          cout<< "You Win!" <<endl;
          return 2 * money;
     }
     cout<<"You loose " << money << " dollars." <<endl;
     return -1 * money;
}

//handles program initializations
void ini(void)
{
     srand(time(0));
}

in line
while(userResponse = menu())

it's very confusing to me at the moment..please can u explain this to me?and I'll probably need more help with this example so please be patiant with me.
thanx in advance.

Infinite Recursion · Oct 4th, 2005, 10:35 AM

The while(userResponse = menu()) line is used to repeat the menu of choices until the user presses 0, which exits the snail races.

OpenLoop · Oct 4th, 2005, 10:38 AM

this about it this way, what does this do:

(Toggle Plain Text)

userResponse = menu();

is sets the variable called userResponse to whatever is returned from the function menu. So if the user pick option 3, userResponse will be set to 3.

In

(Toggle Plain Text)

while(userResponse = menu())

, any number other than zero is considered true, thus any userResponce we get will keep the loop running EXCEPT when the user enters zero. Then the loop will break and probably the program will end.

stevengs · Oct 4th, 2005, 10:38 AM

Simple... while tests, in this case, the result of the assignment expression.

An assignment in C and C++ returns with the value that was assigned. In this case, when menu() is called, and the user inputs 0, userResponse is assigned the value zero. THEN the result of the assignment statement: "userResponse = menu()", which is zero as well, is passed to while for scrutiny. Inherent to C++, false = 0, so the loop is stopped. Any other value is considered true, and the loop would continue.

An assignment always returns the value assigned (*achtung, maybe not when the = operator is overloaded..

)

Which is why

(Toggle Plain Text)

a = b = c = 0;

sets all three variables to 0.
(c = 0) returns with 0, which is then passed to (b = (c = 0)) etc.

Polyphemus_ · Oct 4th, 2005, 10:45 AM

(Toggle Plain Text)

while(userResponse = menu()) {

}

is equal to

(Toggle Plain Text)

while(1) { // loop for ever
 int userResponse = menu();
 if (!userResponse)
  break;

 // put the rest of the loop here
}

InfoGeek · Oct 4th, 2005, 11:03 AM

or

(Toggle Plain Text)

do
{
   userresponse=menu();
   ....
   ....
}while(userresponse);

DaWei · Oct 4th, 2005, 11:24 AM

The "do" is not the same as the "while". If 'userresponse" was zero going in, the while would never be executed, the do will be executed at least once. Close, but no kewpie doll. That's why there are two forms.

ARTillery · Oct 4th, 2005, 12:04 PM

thank u very much for your answer.

Quote:

, any number other than zero is considered true

well, that one is new for me..that's why I thought that the result of this line maybe 2 or 3..and that isn't 0 or 1 which I thought they are a must.

I'm still fighting to understand the whole program but now I have another quick question.

in the previous program..what does ini() function does??I removed this line from the code, and it worked just fine.

stevengs · Oct 4th, 2005, 12:10 PM

it calls srand(), which sets the random number generator's seed (in this case seeded with the current time). I think you need to add

(Toggle Plain Text)

#include <cstdlib>

at the top with the other includes to get srand().

The seed helps the rand() function produce numbers of greatest possible randomness. There are better sources for the seed, but for most cases, the current time suffices.

CSTDLIB library reference

*Back to the original question, it is important that you understand that the assignment statement is returning the value that it assigns. This return value is what the while construct tests.

OpenLoop · Oct 4th, 2005, 1:04 PM

Quote:

Originally Posted by ARTillery

what does ini() function does??I removed this line from the code, and it worked just fine.

If you do that, you will get the same winner everytime you restart your program because the random seed will be constant.

Oct 4th, 2005, 10:28 AM	#1
ARTillery Newbie Join Date: Sep 2005 Posts: 17 Rep Power: 0	While statement Hi all, I'm back again with another question her's a program from the book I'm studying to learn C++ (C++ programming for the absolute beginner), in this program the programmer uses a while loop..from what I understand while tests a condition and if it's true, it continues to perform whatever it's supposed to do.. here in the example..the while doesn't test anything..the programmer just assigned a value to a variable.. (Toggle Plain Text) //4.4 - The Snail Racing Game -Dirk Henkemans //and Mark Lee - Premier Press #include <iostream> #include <ctime> using namespace std; //function declarations int main(void); int race(int, int); void race(void); int menu(void); int placeBet(int); void ini(void); //variables int money = 200; //the main function int main(void) { ini(); int userResponse; cout<< "Welcome to the snail races!!!" <<endl; while(userResponse = menu()) { switch(userResponse) { case 1: case 2: case 3: ::money += race(placeBet(userResponse), userResponse); break; case 4: //the user did not bet race(); break; } } return 0; } //displays the main menu and //returns the user�s selection int menu(void) { int UR;//userResponse; cout << "You have " << money << " dollars."<< endl; do { cout<< "Races Menu" <<endl << "1) Bet on snail 1" << endl << "2) Bet on snail 2" << endl << "3) Bet on snail 3" << endl << "4) Just Watch" << endl << "0) leave the races" << endl; cin>> UR; } while(UR < 0 && UR > 4); return UR; } //decides how much a person will bet on the snail int placeBet(int userResponse) { int betAmount; cout<< "Snail " << userResponse << " is a good choice!" << endl; cout<< "How much would you like to bet on your snail " << userResponse <<"?"; cin >> betAmount; return betAmount; } //if they are just watching the race void race (void) { race(0, 0); } //if they are betting money int race (int money, int userResponse) { //stores the random number int winner = rand() % 3 + 1; cout<< "And the snails are off" << endl << "Look at them GO!!!" << endl << "The winner is snail " << winner; if(winner == userResponse) { cout<< "You Win!" <<endl; return 2 * money; } cout<<"You loose " << money << " dollars." <<endl; return -1 * money; } //handles program initializations void ini(void) { srand(time(0)); } //4.4 - The Snail Racing Game -Dirk Henkemans //and Mark Lee - Premier Press #include <iostream> #include <ctime> using namespace std; //function declarations int main(void); int race(int, int); void race(void); int menu(void); int placeBet(int); void ini(void); //variables int money = 200; //the main function int main(void) { ini(); int userResponse; cout<< "Welcome to the snail races!!!" <<endl; while(userResponse = menu()) { switch(userResponse) { case 1: case 2: case 3: ::money += race(placeBet(userResponse), userResponse); break; case 4: //the user did not bet race(); break; } } return 0; } //displays the main menu and //returns the user�s selection int menu(void) { int UR;//userResponse; cout << "You have " << money << " dollars."<< endl; do { cout<< "Races Menu" <<endl << "1) Bet on snail 1" << endl << "2) Bet on snail 2" << endl << "3) Bet on snail 3" << endl << "4) Just Watch" << endl << "0) leave the races" << endl; cin>> UR; } while(UR < 0 && UR > 4); return UR; } //decides how much a person will bet on the snail int placeBet(int userResponse) { int betAmount; cout<< "Snail " << userResponse << " is a good choice!" << endl; cout<< "How much would you like to bet on your snail " << userResponse <<"?"; cin >> betAmount; return betAmount; } //if they are just watching the race void race (void) { race(0, 0); } //if they are betting money int race (int money, int userResponse) { //stores the random number int winner = rand() % 3 + 1; cout<< "And the snails are off" << endl << "Look at them GO!!!" << endl << "The winner is snail " << winner; if(winner == userResponse) { cout<< "You Win!" <<endl; return 2 * money; } cout<<"You loose " << money << " dollars." <<endl; return -1 * money; } //handles program initializations void ini(void) { srand(time(0)); } in line while(userResponse = menu()) it's very confusing to me at the moment..please can u explain this to me?and I'll probably need more help with this example so please be patiant with me. thanx in advance.

Oct 4th, 2005, 10:35 AM	#2
Infinite Recursion Programming Guru Join Date: Jul 2004 Location: United States Posts: 3,467 Rep Power: 8	The while(userResponse = menu()) line is used to repeat the menu of choices until the user presses 0, which exits the snail races. __________________ http://jasonpowers.net "There are a thousand hacking at the branches of evil to one who is striking at the root."

Oct 4th, 2005, 10:38 AM	#3
OpenLoop Expert Programmer Join Date: May 2005 Location: East Lansing, MI Posts: 663 Rep Power: 4	this about it this way, what does this do: (Toggle Plain Text) userResponse = menu(); userResponse = menu(); is sets the variable called userResponse to whatever is returned from the function menu. So if the user pick option 3, userResponse will be set to 3. In (Toggle Plain Text) while(userResponse = menu()) while(userResponse = menu()) , any number other than zero is considered true, thus any userResponce we get will keep the loop running EXCEPT when the user enters zero. Then the loop will break and probably the program will end.

Oct 4th, 2005, 10:38 AM	#4
stevengs Professional Programmer Join Date: May 2005 Location: Bad Nauheim, Germany Posts: 436 Rep Power: 4	Simple... while tests, in this case, the result of the assignment expression. An assignment in C and C++ returns with the value that was assigned. In this case, when menu() is called, and the user inputs 0, userResponse is assigned the value zero. THEN the result of the assignment statement: "userResponse = menu()", which is zero as well, is passed to while for scrutiny. Inherent to C++, false = 0, so the loop is stopped. Any other value is considered true, and the loop would continue. An assignment always returns the value assigned (achtung, maybe not when the = operator is overloaded.. ) Which is why (Toggle Plain Text) a = b = c = 0; a = b = c = 0; sets all three variables to 0. (c = 0) returns with 0, which is then passed to (b = (c = 0)) etc. __________________ -Steven "Is this a piece of your brain?" - Basil Fawlty Last edited by stevengs; Oct 4th, 2005 at 10:54 AM.*

Oct 4th, 2005, 10:45 AM	#5
Polyphemus_ Expert Programmer Join Date: Aug 2005 Location: Rotterdam, the Netherlands Posts: 942 Rep Power: 4	(Toggle Plain Text) while(userResponse = menu()) { } while(userResponse = menu()) { } is equal to (Toggle Plain Text) while(1) { // loop for ever int userResponse = menu(); if (!userResponse) break; // put the rest of the loop here } while(1) { // loop for ever int userResponse = menu(); if (!userResponse) break; // put the rest of the loop here }

Oct 4th, 2005, 11:03 AM	#6
InfoGeek Professional Programmer Join Date: Jun 2005 Location: India, The great. Posts: 435 Rep Power: 4	or (Toggle Plain Text) do { userresponse=menu(); .... .... }while(userresponse); do { userresponse=menu(); .... .... }while(userresponse); __________________ PFO - My daily dose of technology.

Oct 4th, 2005, 11:24 AM	#7
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	The "do" is not the same as the "while". If 'userresponse" was zero going in, the while would never be executed, the do will be executed at least once. Close, but no kewpie doll. That's why there are two forms. __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

Oct 4th, 2005, 12:10 PM	#9
stevengs Professional Programmer Join Date: May 2005 Location: Bad Nauheim, Germany Posts: 436 Rep Power: 4	it calls srand(), which sets the random number generator's seed (in this case seeded with the current time). I think you need to add (Toggle Plain Text) #include <cstdlib> #include <cstdlib> at the top with the other includes to get srand(). The seed helps the rand() function produce numbers of greatest possible randomness. There are better sources for the seed, but for most cases, the current time suffices. CSTDLIB library reference Back to the original question, it is important that you understand that the assignment statement is returning the value that it assigns. This return value is what the while construct tests. __________________ -Steven "Is this a piece of your brain?" - Basil Fawlty Last edited by stevengs; Oct 4th, 2005 at 12:24 PM.*

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Programming Forums > Application Development > C++

While statement