Why does this always return same number?

Pages: 12
turke (52)
I've wrote a small function and included random number generator but it always returns the same number... WHY???

color = rand() % 4 + 1;

Bazzy (6281)
Are you calling srand()?
Sathed (45)
There's no way (as far as I know) to create a REAL random number in C++. However... You can try this:

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int seed = static_cast<int>(time(0));
srand(seed);


This will create a random number based off of your computer clock. It's not a REAL random number, but it won't produce the same number every time.
Brutal (14)
try
color = 1 + rand() % 4;

it will take a random number, divide it by 4 displaying the remainder which will be 0-3.. add the +1 at the beginning that way it will 1-4, at least what I am understanding from my book anyhow.
helios (17607)
You can do all that static_cast crap, or you can do this:
srand(time(0));
Some prefer to use NULL instead of zero. I like zero.
turke (52)
of course i used srand...
i still can't produce random number by this...
it's similair to this: 
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#include <cstdlib>
#include <iostream>
#include <time.h>
#include <string>

using namespace std;

int main(int argc, char *argv[])
{
    int color;
    srand ( time(NULL) );
    color = rand() % 4 + 1; 
    cout << color;
    return 0;
   }

closed account (z05DSL3A)
So what do you get as ouput with code like:
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#include <cstdlib>
#include <iostream>
#include <time.h>
#include <string>

using namespace std;

int main(int argc, char *argv[])
{
    int color;
    srand ( (unsigned) time(NULL) );
    for(int i= 0;i < 50; i++)
    {
        color = rand() % 4 + 1; 
        cout << color <<endl;
    }
    return 0;
}
turke (52)
@ Grey Wolf
It works but i still don't understand how to use it...
I'm trying to make something like random card generator for a Blackjack program I'm trying to make xD...

It looks like this so if you could help I would really appreciate your help...
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#include <cstdlib>
#include <iostream>
#include <time.h>
#include <string>

using namespace std;

int main(int argc, char *argv[])
{
    //INITIALIZE
    int color,value;
    string value_str,color_str;
    srand ( (unsigned) time(NULL) );

    
    //RANDOM COLOR
    color = rand() % 4 + 1; 
    if (color = 1)
    color_str = "Heart";
    else if (color = 2)
    color_str = "Diamond";
    else if (color = 3)
    color_str = "Club";
    else
    color_str = "Spade";
    
    //RANDOM VALUE
    value = rand() % 13 + 1;
    if (value=1)
    value_str = "Ace";
    else if (value = 2)
    value_str = "2";
    else if (value = 3)          
    value_str = "3";          
    else if (value = 4)
    value_str = "4";
    else if (value = 5)
    value_str = "5";
    else if (value = 6)
    value_str = "6";
    else if (value = 7)
    value_str = "7";
    else if (value = 8)
    value_str = "8";
    else if (value = 9)
    value_str = "9";
    else if (value = 10)
    value_str = "10";
    else if (value = 11)
    value_str = "Jack";
    else if (value = 12)
    value_str = "Queen";
    else
    value_str = "King";
    
    //DISPLAY
    cout << color_str << " " << value_str << endl;
        
    //END           
    system("PAUSE");
    return EXIT_SUCCESS;
}
Bazzy (6281)
All the if conditions are wrong, you should use the == operator ( if (value==1) )

You can use a switch instead of many if-else
Last edited on
turke (52)
OMG I can't believe I didn't put double ==...
*ashamed*
Ty man =)...
P.S.Since you can see I am total noob could you possibly explain me how to use switch?
Bazzy (6281)
switch works for integral types as follows:
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switch( Variable )
{
    case 1:
        //Variable == 1
        break;//as you have to put break you don't need braces
    case 2: //if the break is not found it will perform the next case
    case 3:
       //Variable == 2 || Variable == 3
       break;
    default:
       //All other values
}




http://www.cplusplus.com/doc/tutorial/control.html#switch
Last edited on
turke (52)
OK ty I get it now...
I made FINALLY that random card generator and I made a "Hit" like in BJ...
The problem is that i don't know where to define points = 0 because if I don't points get messed up and if I define them in void they always get restarted but if I define points value in main function, void doesn't recognize it... HELP!!!!
Btw, this is still in If-Else form, I'll fix it afterward I'm too lazy to do it now =P
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#include <cstdlib>
#include <iostream>
#include <time.h>
#include <string>

using namespace std;

void Random ();

int main(int argc, char *argv[])
{   
    Random ();           
    system("PAUSE");
    return EXIT_SUCCESS;
}


void
Random ()
{
    //INITIALIZE
    int color,value,points;
    string value_str,color_str,t;
    srand (time(0));

    
   
    //RANDOM COLOR
    color = rand() % 4 + 1; 
    if (color == 1) 
    color_str = "Heart";
    else if (color == 2)
    color_str = "Diamond";
    else if (color == 3)
    color_str = "Club";
    else
    color_str = "Spade";
    
    //RANDOM VALUE
    value = rand() % 13 + 1;
    if (value == 1)
    {
    value_str = "Ace";
    points = points + 11;
}
    else if (value == 2)
    {
    value_str = "2";
    points = points + 2;
}
    else if (value == 3)          
    {
    value_str = "3"; 
    points = points + 3;
}         
    else if (value == 4)
    {
    value_str = "4";
    points = points + 4;
}
    else if (value == 5)
    {
    value_str = "5";
    points = points + 5;
}
    else if (value == 6)
    {
    value_str = "6";
    points = points + 6;
}
    else if (value == 7)
    {
    value_str = "7";
    points = points + 7;
}
    else if (value == 8)
    {
    value_str = "8";
    points = points + 8;
}
    else if (value == 9)
    {
    value_str = "9";
    points = points + 9;
}
    else if (value == 10)
    {
    value_str = "10";
    points = points + 10;
}
    else if (value == 11)
    {
    value_str = "Jack";
     points = points + 10;
}
    else if (value == 12)
    {
    value_str = "Queen";
     points = points + 10;
}
    else
    {
    value_str = "King";
     points = points + 10;
}

    
        
    //DISPLAY
    cout << color_str << " " << value_str << endl;

       
    //HIT OR STAY
    cout << "Points :" << points << endl;
    cout << "Hit (t) or Stay (s)?" << endl;
    cin >> t;
    if (t == "t")
    Random ();
}
eker676 (427)
Define any variable you want accessible to the whole program outside and before the main function.

i.e.
#include <iostream>
int somevariable = 0;

int main()
turke (52)
ok tnx and how can i make this end here???

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if (points <= 21)
    cout << color_str << " " << value_str << endl;
    else
    {
    cout << "Points :" << points << endl;
    cout << "Looser!" << endl;
    ?????????????????????????????
    }
Last edited on
helios (17607)
return 0?
turke (52)
Don't you think I already tried that?
Compiler says : "return statement with a value,in function returning void"...
Bazzy (6281)
return; without any value
turke (52)
weeeeeee tnx m8 =))
turke (52)
I think I've done most of it I would just appreciate if someone could explain me how to use switches instead of else-ifs and how to make cards not so repetitive and also, the most important, HOW TO DISABLE MAKING SAME CARDS MULTIPLE TIMES???
i.e.
Spade 2
Spade 2
Club 2
Heart 5
Spade 2
etc...

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#include <cstdlib>
#include <iostream>
#include <time.h>
#include <string>

using namespace std;

void Random (), Random_PC ();
int points=0;


int main(int argc, char *argv[])
{   
    Random ();           
    system("PAUSE");
    return EXIT_SUCCESS;
         
}


void
Random ()
{
    //INITIALIZE
    int color,value,PC_points;
    string value_str,color_str,t;
    srand((unsigned)time(0) );

       
    //RANDOM COLOR
    color = rand() % 4 + 1; 
   
    if (color == 1) 
    color_str = "Heart";
    else if (color == 2)
    color_str = "Diamond";
    else if (color == 3)
    color_str = "Club";
    else
    color_str = "Spade";
   
   
     
    //RANDOM VALUE
    value = rand() % 13 + 1;
    if (value == 1)
    {
    value_str = "Ace";
    points = points + 11;
}
    else if (value == 2)
    {
    value_str = "2";
    points = points + 2;
}
    else if (value == 3)          
    {
    value_str = "3"; 
    points = points + 3;
}         
    else if (value == 4)
    {
    value_str = "4";
    points = points + 4;
}
    else if (value == 5)
    {
    value_str = "5";
    points = points + 5;
}
    else if (value == 6)
    {
    value_str = "6";
    points = points + 6;
}
    else if (value == 7)
    {
    value_str = "7";
    points = points + 7;
}
    else if (value == 8)
    {
    value_str = "8";
    points = points + 8;
}
    else if (value == 9)
    {
    value_str = "9";
    points = points + 9;
}
    else if (value == 10)
    {
    value_str = "10";
    points = points + 10;
}
    else if (value == 11)
    {
    value_str = "Jack";
     points = points + 10;
}
    else if (value == 12)
    {
    value_str = "Queen";
     points = points + 10;
}
    else
    {
    value_str = "King";
     points = points + 10;
}

    
        
    //DISPLAY
    if (points <= 21)
    cout << color_str << " " << value_str << endl;
    else
    {
    cout << "Points :" << points << endl;
    cout << "Looser!" << endl;
    return;
    }
    
    

       
    //HIT OR STAY
    cout << "Points :" << points << endl;
    cout << "Hit (t) or Stay (s)?" << endl;
    cin >> t;
    if (t == "t")
    Random ();
    if (t == "s")
    {
      again:
             PC_points = rand() % 35 + 1;
      if (PC_points < 18)
      goto again;
      cout << "PC Points: " << PC_points << endl;
      if (points < PC_points)
      cout << "Looser!" << endl;
      else if (points > PC_points)
      cout << "Winner!" << endl;
      else 
      cout << "Draw!" << endl;
      } 
}


ty
Last edited on
Bazzy (6281)
Move srand in main before the Random call.

Lines 135-138 should better be
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do
    PC_points = rand() % 35 + 1;
while(PC_points < 18);



If you want to use a switch you could do it this way:
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switch(value)
{
    case 1:
        value_str = "Ace";
        points = points + 11;
        break;
    case 2:
        value_str = "2";
        points = points + 2;
        break;
    //...
}
It was ony a suggestion, if you like you can keep the if-else
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