C++ class and function output issue - c++

Question

I'm having problems with my program's output. It keeps spitting out 12345.
Here's the details:
It's split in three files: program8.cpp (the part that runs tests), myRandom.cpp (implementation of the class), and myRandom.h (specification of the class).
myRandom.h:
#ifndef MYRANDOM_H_
#define MYRANDOM_H_
class myRandom
{
public:
myRandom(); //Constructor
~myRandom(); //Destructor
void seed(unsigned long theSeed); //Mutator for current
unsigned long next(); //Mutator or Accessor for current
int randInt(int start, int end); //Scales result to a range
double randNormal(); //Future expansion
private:
unsigned long current; //Current random #
static const unsigned long a = 1103515245; //Multiplier for LGC
static const unsigned long c = 12345; //Increment for LGC
static const unsigned long m = 2147483648; //Modulus for LGC
};
#endif /* MYRANDOM_H_ */
myRandom.cpp:
#include <iostream>
#include <cstdlib>
#include "myRandom.h"
using namespace std;
myRandom::myRandom() //Constructor
{
current = 0;
}
myRandom::~myRandom() //Destructor
{
}
void myRandom::seed(unsigned long theSeed) //Mutator for current
{
if (theSeed < 0 || theSeed > m-1)
{
// ERROR
return;
}
else
current = theSeed;
}
unsigned long myRandom::next() //Mutator or Accessor for current
{
if (current < 0)
{
cout << "Error: cannot set seed to a negative number" << endl;
return 0;
}
else
{
current = (m*current+c)%m; //Formula
return current;
}
}
int myRandom::randInt(int start, int end) //Scales result to a range
{
if (start >= end)
{
cout << "Error: cannot set start greater than or equal to end" << endl;
return 0;
}
else
{
return ((this->next() % (end - start)) + start);
}
}
double myRandom::randNormal() //Future expansion
{
cout << "Warning: randNormal not implemented" << endl;
return 0;
}
program8.cpp:
#include <iostream>
#include <cstdlib>
#include "myRandom.h"
using namespace std;
int main()
{
myRandom theRand;
unsigned long theSeed;
cout << "Verify that the sequence generated by next() is the same on each run" << endl;
for (int i = 0; i < 5; i++)
{
cout << theRand.next() << endl;
}
cout << "Verify that you can set the seed to 0 and 1" << endl;
theSeed = 0;
cout << theRand.next() << endl;
theSeed = 1;
cout << theRand.next() << endl;
cout << "Verify that attempting to set the seed to -1 generates an error" << endl;
theSeed = -1;
cout << theRand.next() << endl;
cout << "Verify that you can set the seed to m-2 and m-1" << endl;
theSeed = 2147483648-2;
cout << theRand.next() << endl;
theSeed = 2147483648-1;
cout << theRand.next() << endl;
cout << "Verify that attempting to set the seed to m generates and error" << endl;
theSeed = 2147483648;
cout << theRand.next() << endl;
cout << "Verify that next() produces a sequence predicted by hand/calc for the chosen seed" << endl;
cout << "Please enter a seed: ";
cin >> theSeed;
cout << theRand.next() << endl;
cout << "Verify that using start == end generates and error. Set both to 10." << endl;
theRand.randInt(10,10);
cout << theRand.next() << endl;
cout << "Verify that using start > end generates and error. Set start to 10 and end to 5." << endl;
theRand.randInt(10,5);
cout << theRand.next() << endl;
theRand.seed(theSeed);
cout << "Testing randInt for start=0 end=1,000" << endl;
for (int i = 0; i < 5; i++)
{
cout << theRand.randInt(0 , 1000) << endl;
}
return 0;
}
I think the problem lies in the next() function, since that's what gets called all those times in program8.cpp cout statements. I could understand getting 12345 once, but it should be updated once that function runs successive times. I apologize if it's a dumb question. Thank you for your time and patience.

Answer 1

Your problem isn't a code specific one - it is Math-related from here:
current = (m*current+c)%m;
This always returns the value of c if c < m, otherwise (or more generally) it returns c % m. Why? From this theorem:
(m*n + a)%m = a
Example:
m = 10
n = 3
a = 7
(10*3 + 7)%10 = 7
See this for more:
http://en.wikipedia.org/wiki/Modulo_operation