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Random number??

Posted on 1998-02-14
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Last Modified: 2010-04-10
How do I have Builder (v1.0 for win 95) generate a random number (10 digits long) then have it save it in regnum.dat??
 
thanks
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Question by:4099aol
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18 Comments
 
LVL 3

Accepted Solution

by:
q2guo earned 40 total points
ID: 1182069
#include <fstream.h>
#include <stdlib.h>

main ()
{
   unsigned int i, k;
   unsigned long random_num;
 
   ostream fout("regnum.dat");
   
   randomize();
   i = rand();
   k = rand();

   random_num = i * k;
   fout << random_num << endl;
}
0
 
LVL 22

Expert Comment

by:nietod
ID: 1182070
That random number won't be 10 digits long.

To get 10 digits I would use an alcoritm that gets a number that is 1 digit long and repeat it 10 times.  Like

char RndDigStr[10];

randomize();
for (int i = 0; i < 10; ++i)
   RndDigStr[i] = '0' + (rand() % 10);

this puts 10 random digits in RndDigStr.  In this case the digits are ASCII digit characters from '0' to '9'.  
0
 

Author Comment

by:4099aol
ID: 1182071
nietod...

You said that the number will be put in the string RndDigStr, well how do I put the numbers in to the dat file?
0
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LVL 22

Expert Comment

by:nietod
ID: 1182072
In my previous example you could make RndDigStr a NUL terminated sting by declaring it length 11 and adding a NUL terminator with

RndDigStr[10] = 0;

then you could output it with

fout << RndDigStr;

or you could forget RndDigStr and output each digit, like

for (int i = 0; i < 10; ++i)
   fout << (char) '0' + (rand() % 10);


0
 

Author Comment

by:4099aol
ID: 1182073
so do this??

{                          
ostream fout("regnum.dat");
                             
char RndDigStr[10];

randomize();
for (int i = 0; i < 10; ++i)
RndDigStr[i] = '0' + (rand() % 10);
fout << RndDigStr;
}
0
 
LVL 22

Expert Comment

by:nietod
ID: 1182074
Not quite.

fout << RndDigStr

will work only if RndDigStr is NUL terminated.  So you would need

{
   ostream fout("regnum.dat");
                               
   char RndDigStr[11]; // Extra room for NUL.

   randomize();
   for (int i = 0; i < 10; ++i)
      RndDigStr[i] = '0' + (rand() % 10);

   RndDigStr[10] = 0; // Terminate.
   fout << RndDigStr;
}

however, if you don't need to save a copy of the digits, drop RndDigStr and just use.

{
   ostream fout("regnum.dat");
                               
   randomize();
   for (int i = 0; i < 10; ++i)
   {
      char chr = '0' + (rand() % 10);

      fout << chr;
   }
}

0
 

Author Comment

by:4099aol
ID: 1182075
Error.  (on both sets of codes)

[C++ Error] webmaster.cpp(81): Could not find a match for 'ostream::ostream(char *)'.
[C++ Warning] webmaster.cpp(86): Conversion may lose significant digits.


0
 
LVL 3

Expert Comment

by:q2guo
ID: 1182076
AnsiString S;
S.SetLength(11);

randomize();

for (int i = 0; i < 10; ++i)
{
   S[i] = '0' + (rand() % 10);
}
S[10] = '\0';

TStringList *MyStringList = new TStringList;
MyStringList->Add(S);
MyStringList->SaveToFile("regnum.dat");
0
 

Author Comment

by:4099aol
ID: 1182077
I am now getting this popup dialog box...

Project webmaste1.exe rasied exception class EOutOfMemory with message 'Out of Memory'.

I restarted my computer (thinking my computer was just running low on RAM, but had the same message.  I took the codes (that u just gave me) out and the app works fine.  Please tell me how do I get it to manage it's memory a little bit better, or fix the codes to sue less memory.
0
 
LVL 22

Expert Comment

by:nietod
ID: 1182078
Sorry I don't use streams so I wasn't aware that you can't print a "const char *" with a stream.  q2quo's string class solution should work.  Although I've never heard of "AnsiString", the strig supplied by STL that I'm aware of is just called "string".  But I'm not too familiare with STL.

as for th warning about loosing digits, ignore it or use the "(char)" conversion operator.  That is change

char chr = '0' + (rand() % 10);

to

char chr = (char) '0' + (rand() % 10);


0
 
LVL 3

Expert Comment

by:q2guo
ID: 1182079
Add
delete MyStringList;
to the end of my code
so it should read

.
.
.

TStringList *MyStringList = new TStringList;
MyStringList->Add(S);
MyStringList->SaveToFile("regnum.dat");
delete MyStringList;
0
 

Author Comment

by:4099aol
ID: 1182080
nope still out of memory
0
 
LVL 3

Expert Comment

by:q2guo
ID: 1182081
Are your running above code inside a loop?
0
 

Author Comment

by:4099aol
ID: 1182082
I do not think so, it is in FormCreate (Borland C++ Builder)
0
 

Expert Comment

by:larockd
ID: 1182083
Is randomize() a function specific to Borland?  I think I remember using it in Pascal..

Shouldn't he use srand instead to seed the random number generator?  Or does randomize in borland take care of it.  I checked on this in Visual C++ and the closest thing to randomize is randomize() when using vbscript?
0
 

Author Comment

by:4099aol
ID: 1182084
i have no idea.
0
 
LVL 3

Expert Comment

by:q2guo
ID: 1182085
Try this 4099Aol

#include <vcl/classes.hpp>
#include <stdlib.h>

char S[11];
randomize();

for (int i = 0; i < 10; ++i)
{
    S[i] = '0' + (rand() % 10);
}
S[10] = '\0';

AnsiString randstring(S);

TStringList *MyStringList = new TStringList;
MyStringList->Add(S);
MyStringList->SaveToFile("regnum.dat");
0
 

Author Comment

by:4099aol
ID: 1182086
thank you it works!
0

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