im trying to generate a random number using

#include <cstdlib>

and then

srand(time(0));

but it keeps telln me i need a constructor, destructor or type before the (. what do i do??

The time function comes from the <ctime> header (failure to include it is probably your error), and keep in mind that everything in the c* headers should be in the std namespace:

#include <cstdlib>
#include <ctime>

int main()
{
  std::srand ( (unsigned)std::time ( 0 ) );
}

Though some compilers are more lax with that particular namespace requirement, so if you get an error that srand or time are not a part of namespace std, that's why.

Edited 6 Years Ago by Narue: n/a

ok, ill try. im still really new at this.

#include <iostream>
#include <cstdlib>
#include <ctime>
using namespace std;


int N, iTotalMoves, iTotalHome, x, iTotalPub;
float fAverageMoves, fAverageHome, fProbHome;
int B = 1000000;
void Walk(float &fAverageMoves, int &iTotalMoves,
int &iTotalHome, float &fAverageHome, int &N, int &x,
int &iTotalPub, float fProbHome) ;

int Spot;


srand(time(0));


int main()
{
Walk(fAverageMoves, iTotalMoves, iTotalHome, fAverageHome, N, x,
iTotalPub, fProbHome);
return 0;
}

void Walk(float &fAverageMoves, int &iTotalMoves, int &iTotalHome,
float &fAverageHome, int &N, int &x, int &iTotalPub, float fProbHome)
{
fProbHome = rand() % 3;

N=2;

while(2<= N&& 7>=N && N++)
{

if(iTotalHome+iTotalPub <= 1000000)
{N=x;
do
{
if (1< x<8)
{

if(fProbHome == 1 || fProbHome == 2)
{
x=x+1;
}

if(fProbHome == 0)
{
x = x-1;
}
}
}while(x!= 1 && x!= 8);

if(x==1)
{
iTotalHome++;
}
if(x==8)
{
iTotalPub++;
}
iTotalMoves ++;
}
fAverageMoves = iTotalMoves/(N-1);
fAverageHome = iTotalHome/iTotalMoves;
cout << "Average Moves:" << fAverageMoves<< endl;
cout << "Total Home:" << iTotalHome<< endl;
cout << "Total Pub:" << iTotalPub<< endl;
cout << "Total Moves:" << iTotalMoves<< endl;
}
return;
}

bash-3.2$ fg++ program4.cpp -o program4
program4.cpp:27: error: expected constructor, destructor, or type conversion before ‘(’ token

does that help at all?

srand(time(0));


int main()
{
    Walk(fAverageMoves, iTotalMoves, iTotalHome, fAverageHome, N, x,
    iTotalPub, fProbHome); 
    return 0;
}

You are trying to call functions outside of any function. Put srand(time(0)); inside main.

Edited 6 Years Ago by nezachem: n/a

i fixed it! i had to put the list of variables inside the int main().
then it worked

ok im stuck now.

this is what im supposed to do:
The classic drunkard's walk problem: Over an eight block line,
the home of an intoxicated chap is at block 8, and a pub is at block 1.
Our poor friend starts at block n, 2 <= n <= 7, and wanders at random,
one block at a time, either toward or away from home. At any intersection,
he moves toward the pub with a certain probability, say 2/3, and towards
home with a certain probability, say 1/3. Having gotten either home or to
the pub, he remains there. Write a program to simulate 1000000 trips in which
he starts at block 2, another 1000000 in which he starts at block 3, and so
forth up through block 7. For each starting point, calculate and print the
proportion of the time he ends up at home and the average number of blocks
he walked on each trip.

For the random number generation...

Use the 'srand' function to seed the random number generator.
Use the 'rand' function (and mod as needed) to get random probabilities
for a given step.
To do each single walk, call a function that runs through a loop
until the walk is done.

and im supposed to get approximately this:


I = 2
TotalMoves = 2834110
Avg moves = 2.834110
total Home = 7820
avg home = 0.0078200


I = 3
TotalMoves = 5503639
Avg moves = 5.503639
total Home = 23621
avg home = 0.0236210


I = 4
TotalMoves = 7830959
Avg moves = 7.830959
total Home = 54851
avg home = 0.0548510


I = 5
TotalMoves = 9519658
Avg moves = 9.519658
total Home = 118166
avg home = 0.1181660


I = 6
TotalMoves = 9875095
Avg moves = 9.875095
total Home = 243413
avg home = 0.2434130


I = 7
TotalMoves = 7581532
Avg moves = 7.581532
total Home = 496420
avg home = 0.4964200


ill post what i have now in another reply

#include <iostream>
#include <cstdlib>
#include <ctime>
using namespace std;

int main()
{
int N, iTotalMoves, iTotalHome, x, iTotalPub, iProbHome;
float fAverageMoves, fAverageHome;
void Walk(float &fAverageMoves, int &iTotalMoves,
int &iTotalHome, float &fAverageHome, int &N, int &x,
int &iTotalPub, int iProbHome) ;

srand(time(0));

Walk(fAverageMoves, iTotalMoves, iTotalHome, fAverageHome, N, x,
iTotalPub, iProbHome);


return 0;


}

void Walk(float &fAverageMoves, int &iTotalMoves, int &iTotalHome,
float &fAverageHome, int &N, int &x, int &iTotalPub, int iProbHome)
{

N=2;
iTotalHome=0;
iTotalPub=0;
do
{

if(iTotalHome+iTotalPub <= 1000000&& iTotalHome+iTotalPub >=0)
{

N=x;
do
{

iProbHome = rand()%3;

if(iProbHome == 1 || iProbHome == 2)
{
x=x+1;
iTotalMoves++;
}

if(iProbHome == 0 && x != 1 && x !=8)
{
x = x-1;
iTotalMoves++;
}

}while(x!= 1 && x!= 8);

if(x==1)
{
iTotalHome++;
}
if(x==8)
{
iTotalPub++;
}


}


fAverageMoves = iTotalMoves/1000000;
fAverageHome = iTotalHome/1000000;
cout << "I = " << N << endl;
cout << "Average Moves:" << fAverageMoves<< endl;
cout << "Total Home:" << iTotalHome<< endl;
cout << "Average Home:" << fAverageHome << endl;
cout << "Total Moves:" << iTotalMoves<< endl<< endl;

N++;

}while(2<=N && 7>=N);

return;

can anybody help me?

omg, use code tags.
[-code][/-code]
without the dashes, that'd make people like me want to help you ;D

Edited 6 Years Ago by Excizted: n/a

like this?

#include <iostream>
#include <cstdlib>
#include <ctime>
using namespace std;

int main()
{
int N, iTotalMoves, iTotalHome, x, iTotalPub, iProbHome;
float fAverageMoves, fAverageHome;
void Walk(float &fAverageMoves, int &iTotalMoves, 
int &iTotalHome, float &fAverageHome, int &N, int &x,
int &iTotalPub, int iProbHome) ;

srand(time(0));



Walk(fAverageMoves, iTotalMoves, iTotalHome, fAverageHome, N, x,
iTotalPub, iProbHome); 


return 0;


}

void Walk(float &fAverageMoves, int &iTotalMoves, int &iTotalHome,
float &fAverageHome, int &N, int &x, int &iTotalPub, int iProbHome)
{

N=2;
iTotalHome=0;
iTotalPub=0;
do
{ 

if(iTotalHome+iTotalPub <= 1000000&& iTotalHome+iTotalPub >=0) 
{

N=x;
do
{

iProbHome = rand()%3;

if(iProbHome == 1 || iProbHome == 2)
{ 
x=x+1;
iTotalMoves++;
}

if(iProbHome == 0 && x != 1 && x !=8)
{
x = x-1; 
iTotalMoves++;
} 

}while(x!= 1 && x!= 8);

if(x==1)
{
iTotalHome++;
}
if(x==8)
{
iTotalPub++;
}


}


fAverageMoves = iTotalMoves/1000000;
fAverageHome = iTotalHome/1000000;
cout << "I = " << N << endl;
cout << "Average Moves:" << fAverageMoves<< endl;
cout << "Total Home:" << iTotalHome<< endl;
cout << "Average Home:" << fAverageHome << endl;
cout << "Total Moves:" << iTotalMoves<< endl<< endl;

N++;

}while(2<=N && 7>=N);

return;

ok, im closer im gettin roughly desireable answers but for every step its just repeating the same as the last. its not changing at all

yea. i cant get my loop right to make it ontinue to add to the variables.

#include <iostream>
#include <ctime>
#include <cstdlib>
using namespace std;

int main()
{

  int N;
  float iTotalHome, iTotalMoves, iProbHome, x;
  float fAverageMoves, fAverageHome;
  void Walk(float &fAverageMoves, float &iTotalMoves, float &iTotalHome, 
    float &fAverageHome, int &N, float &x, float &iProbHome);
  
  srand(time(0));
  
Walk(fAverageMoves, iTotalMoves, iTotalHome, fAverageHome, N, x,
iProbHome);

return 0;
}


void Walk(float &fAverageMoves, float &iTotalMoves, float &iTotalHome, float
  &fAverageHome, int &N, float &x, float &iProbHome)
{
int T;
do
{
  cout<< "Please enter the block number starting with 2 and ending with 7. One"<< endl;
  cout <<  " at a time." << endl;
  cin >> N;
  x=N;
  for(T=1000000; 0<=T; T--)
  {
   iProbHome = rand()%3;
   
     if(iProbHome == 1 || iProbHome == 2 && x!=1 && x!=8)
       {
       x++;
       iTotalMoves++;
       }
     if(iProbHome ==0&& x!= 1 && x!= 8)
      {
      x--;
      iTotalMoves++;
      }
   if(x==1)
   iTotalHome++;
   
   
   iProbHome=0;
  }
  fAverageHome=iTotalHome/1000000;
  fAverageMoves= iTotalMoves/1000000;
  
  cout<< "I = " << N << endl;
  cout<< "Total Moves = " << iTotalMoves << endl;
  cout<< "Average Moves = " << fAverageMoves << endl;
  cout<< "Total Home = " << iTotalHome << endl;
  cout<< "AverageHome = " << fAverageHome << endl;

  


}while(2<=N);

return;
}


thats my most updated code so far.

but heres what its giving me.

Please enter the block number starting with 2 and ending with 7. One
at a time.
2
I = 2
Total Moves = 999996
Average Moves = 0.999996
Total Home = 1
AverageHome = 1e-06
Please enter the block number starting with 2 and ending with 7. One
at a time.
3
I = 3
Total Moves = 1.99999e+06
Average Moves = 1.99999
Total Home = 4
AverageHome = 4e-06
Please enter the block number starting with 2 and ending with 7. One
at a time.
4
I = 4
Total Moves = 2.99999e+06
Average Moves = 2.99999
Total Home = 4
AverageHome = 4e-06
Please enter the block number starting with 2 and ending with 7. One
at a time.
5
I = 5
Total Moves = 3.99999e+06
Average Moves = 3.99999
Total Home = 4
AverageHome = 4e-06
Please enter the block number starting with 2 and ending with 7. One
at a time.
6
I = 6
Total Moves = 4.99999e+06
Average Moves = 4.99999
Total Home = 4
AverageHome = 4e-06
Please enter the block number starting with 2 and ending with 7. One
at a time.
7
I = 7
Total Moves = 6e+06
Average Moves = 6
Total Home = 4
AverageHome = 4e-06
Please enter the block number starting with 2 and ending with 7. One
at a time.
^X exit
I = 7
Total Moves = 6.99999e+06
Average Moves = 6.99999
Total Home = 4
AverageHome = 4e-06
Please enter the block number starting with 2 and ending with 7. One
at a time.


plz plz plz help... ive been working on this for hours and im sooo lost

There's a number of major problems with your code.

I'd highly recommend you to redesign it according the following guidelines:
1. Create a function int make_step(int prob) returning either 1 or -1. Try to understand what rand() does, and how to calculate directions given the probability of walking to the left (so far you don't seem to understand it).
2. Create a function walk(int startpos) returning single walk data. It should continuously invoke make_step to update a position until either a home or a pub is reached.
3. Create a function void simulate(int startpos) which will call walk for 100000 times accumulating the data, and print the statistics.
4. Call simulate for startpos from 2 to 7.

#include <iostream>
#include <cstdlib>
#include <ctime>
using namespace std;

int main()
{
  int N, iTotalMoves; 
  int iTotalHome=0;
  int iTotalPub=0;
  int x, iProbHome;
  float fAverageMoves, fAverageHome;
  
  
  int Prob(int &iProbHome);
  
  
  int StartPos(int &N, int &x, void Walk(int x, int iProbHome,  int &iTotalMoves,
               int &iTotalHome, int &iTotalPub, int Prob(int &iProbHome), void Print(float &fAverageMoves, 
               float &fAveragHome, int iTotalMoves, int iTotalHome)));
  
  
  void Walk(int iProbHome, int x, int &iTotalMoves, int &iTotalHome, 
      int &iTotalPub, float &fAverageMoves, float &fAverageHome, int Prob(int &iProbHome),
      void Print(float &fAverageMoves, float &fAverageHome, int iTotalMoves, int iTotalHome)); 
  
  
  void Print(float &fAverageMoves, float &fAverageHome, int iTotalMoves, int iTotalHome);
 
 srand(time(0));
 

StartPos(N, x, Walk(N, iProbHome, x, iTotalMoves, iTotalHome, iTotalPub, fAverageMoves, fAverageHome,
         Prob(iProbHome)));



return 0;
}




int StartPos(int &N, int &x, void Walk(int x, int iProbHome, int &iTotalMoves, int &iTotalHome, 
             int &iTotalPub, int Prob(int &iProbHome), void Print(float &fAverageMoves, float &fAverageHome,
             int iTotalMoves, int iTotalHome)))
{

cout<< "Please enter a number between two and seven, starting with two" <<endl;
    << "and going up by a single integer until 7 has been inputed." << endl;
cin >> N;


x=N;
if(2<=N&& N<=7)
{

Walk(x, iProbHome, iTotalMoves, iTotalHome, iTotalPub, fAverageMoves, fAverageHome, Prob(iProbHome),
     Print(fAverageMoves, fAverageHome, iTotalMoves, iTotalHome) );
}
return N;

}






int Prob(int &iProbHome)
{

iProbHome = rand()%6;
cout<< iProbHome<< endl;
return iProbHome;

}




void Walk(int iProbHome, int x, int &iTotalMoves, int &iTotalHome, int &iTotalPub,
         int Prob(int &iProbHome), void Print(float &fAverageMoves, float &fAverageHome, 
         int iTotalMoves, int iTotalHome))
{

int T;
T=1000000;
do
{

  
  Prob(iProbHome);
  
  if(iProbHome == 1 || iProbHome == 2 || iProbHome == 3 || iProbHome ==5)
  {
    x=x+1;
    iTotalMoves++;
  }
  
  if(iProbHome == 0 || iProbHome == 4)
  {
   x=x-1;
   iTotalMoves++;
  }
  
  if(x==1)
  {
  iTotalHome++;
  }
  
  if(x==8)
  {
  iTotalPub++;
  }
  
  T--;
}while(T>= 0);
 
Print(fAverageMoves, fAverageHome, iTotalMoves, iTotalHome);

}



void Print(float &fAverageMoves, float &fAverageHome, int iTotalMoves, int iTotalHome)
{

fAverageMoves= iTotalMoves/1000000;
fAverageHome = iTotalHome/1000000;

cout << "I = " << N << endl;
cout << "Average Moves = " << fAverageMoves << endl;
cout << "Total Moves = " << iTotalMoves << endl;
cout << "AverageHome = " << fAverageHome << endl;
cout << "TotalHome = " << iTotalHome << endl;

return;

}
bash-3.2$ ext
bash: ext: command not found
bash-3.2$ exit
exit

Script done on Thu 17 Dec 2009 01:44:25 PM CST

this is what i have now. but im having problems with the functions. am i declaring them wrong?

This article has been dead for over six months. Start a new discussion instead.