C# Rastgele (Random) Sayı Belirleme

Merhaba arkadaşlar, Programlamanın en temel konularından biri de rastgele sayı üretmektir. Siber güvenliğin temelinde rastgele sayı üretme bulunmaktadır.

Bu yazımızda C# ile rastgele sayı üretme üzerinde duracağız.

Rastgele sayı üretiminde kullandığımız sınıf System isim uzayında bulunan Random sınıfıdır. 

Random sınıfına ait iki adet constructor bulunmaktadır.

Random sınıfına ait en çok kullanılan metotları ise aşağıdaki gibidirler.

Örnekler:

Random rnd = new Random();
int or1= rnd.Next(1, 13); // 1 <= or1 < 13
int or2= rnd.Next(1, 7); // 1 <= or2 < 7
int or3 = rnd.Next(52); // 0 <= or3 < 52

NOT: Bir döngü içerisinde (for, while, do-while…) rastgele sayı üretilecekse Random nesnesini muhakkak döngü dışında oluşturmak gerekmektedir. Aksi durumda her defasında aynı seed numarası ile işlem yapacağından aynı sayıyı üretecektir.

Meraklısına 🙂

C# Random sınıfının kendi kodu şöyledir.

namespace System {

using System;
using System.Runtime;
using System.Runtime.CompilerServices;
using System.Globalization;
using System.Diagnostics.Contracts;
[System.Runtime.InteropServices.ComVisible(true)]
[Serializable]
public class Random {
//
// Private Constants
//
private const int MBIG = Int32.MaxValue;
private const int MSEED = 161803398;
private const int MZ = 0;


//
// Member Variables
//
private int inext;
private int inextp;
private int[] SeedArray = new int[56];

//
// Public Constants
//

//
// Native Declarations
//

//
// Constructors
//

public Random()
: this(Environment.TickCount) {
}

public Random(int Seed) {
int ii;
int mj, mk;

//Initialize our Seed array.
//This algorithm comes from Numerical Recipes in C (2nd Ed.)
int subtraction = (Seed == Int32.MinValue) ? Int32.MaxValue : Math.Abs(Seed);
mj = MSEED - subtraction;
SeedArray[55]=mj;
mk=1;
for (int i=1; i<55; i++) { //Apparently the range [1..55] is special (Knuth) and so we're wasting the 0'th position.
ii = (21*i)%55;
SeedArray[ii]=mk;
mk = mj - mk;
if (mk<0) mk+=MBIG;
mj=SeedArray[ii];
}
for (int k=1; k<5; k++) {
for (int i=1; i<56; i++) {
SeedArray[i] -= SeedArray[1+(i+30)%55];
if (SeedArray[i]<0) SeedArray[i]+=MBIG;
}
}
inext=0;
inextp = 21;
Seed = 1;
}

//
// Package Private Methods
//

/*====================================Sample====================================
**Action: Return a new random number [0..1) and reSeed the Seed array.
**Returns: A double [0..1)
**Arguments: None
**Exceptions: None
==============================================================================*/
protected virtual double Sample() {
//Including this division at the end gives us significantly improved
//random number distribution.
return (InternalSample()*(1.0/MBIG));
}

private int InternalSample() {
int retVal;
int locINext = inext;
int locINextp = inextp;

if (++locINext >=56) locINext=1;
if (++locINextp>= 56) locINextp = 1;

retVal = SeedArray[locINext]-SeedArray[locINextp];

if (retVal == MBIG) retVal--;
if (retVal<0) retVal+=MBIG;

SeedArray[locINext]=retVal;

inext = locINext;
inextp = locINextp;

return retVal;
}

//
// Public Instance Methods
//


/*=====================================Next=====================================
**Returns: An int [0..Int32.MaxValue)
**Arguments: None
**Exceptions: None.
==============================================================================*/
public virtual int Next() {
return InternalSample();
}

private double GetSampleForLargeRange() {
// The distribution of double value returned by Sample
// is not distributed well enough for a large range.
// If we use Sample for a range [Int32.MinValue..Int32.MaxValue)
// We will end up getting even numbers only.

int result = InternalSample();
// Note we can't use addition here. The distribution will be bad if we do that.
bool negative = (InternalSample()%2 == 0) ? true : false; // decide the sign based on second sample
if( negative) {
result = -result;
}
double d = result;
d += (Int32.MaxValue - 1); // get a number in range [0 .. 2 * Int32MaxValue - 1)
d /= 2*(uint)Int32.MaxValue - 1 ;
return d;
}


/*=====================================Next=====================================
**Returns: An int [minvalue..maxvalue)
**Arguments: minValue -- the least legal value for the Random number.
** maxValue -- One greater than the greatest legal return value.
**Exceptions: None.
==============================================================================*/
public virtual int Next(int minValue, int maxValue) {
if (minValue>maxValue) {
throw new ArgumentOutOfRangeException("minValue",Environment.GetResourceString("Argument_MinMaxValue", "minValue", "maxValue"));
}
Contract.EndContractBlock();

long range = (long)maxValue-minValue;
if( range <= (long)Int32.MaxValue) {
return ((int)(Sample() * range) + minValue);
}
else {
return (int)((long)(GetSampleForLargeRange() * range) + minValue);
}
}


/*=====================================Next=====================================
**Returns: An int [0..maxValue)
**Arguments: maxValue -- One more than the greatest legal return value.
**Exceptions: None.
==============================================================================*/
public virtual int Next(int maxValue) {
if (maxValue<0) {
throw new ArgumentOutOfRangeException("maxValue", Environment.GetResourceString("ArgumentOutOfRange_MustBePositive", "maxValue"));
}
Contract.EndContractBlock();
return (int)(Sample()*maxValue);
}


/*=====================================Next=====================================
**Returns: A double [0..1)
**Arguments: None
**Exceptions: None
==============================================================================*/
public virtual double NextDouble() {
return Sample();
}


/*==================================NextBytes===================================
**Action: Fills the byte array with random bytes [0..0x7f]. The entire array is filled.
**Returns:Void
**Arugments: buffer -- the array to be filled.
**Exceptions: None
==============================================================================*/
public virtual void NextBytes(byte [] buffer){
if (buffer==null) throw new ArgumentNullException("buffer");
Contract.EndContractBlock();
for (int i=0; i<buffer.Length; i++) {
buffer[i]=(byte)(InternalSample()%(Byte.MaxValue+1));
}
}
}



}