C++ Arrays, Array Conversion not working - c++

Question

I've been stuck on a problem for quite a while today, and despite my searching the internet, I'm not sure as to what I should do. This program (that I will post the source code to) is supposed to be based off of the Birthday Paradox, and help us to prove it correct.
The idea is that we have multiple arrays, one of which simulates the paradox by counting the times that there is NOT a matching birthday pair, another which takes that array and creates a ratio(array value/over total iterations) and another that creates a theoretical array ratio value.
Now, this is where I"m stuck. I can get the first two functions to work perfectly, birthdayFrequency and ratioArray, but the next one idealArray I cannot get to work properly. Both ratioArray and idealArray should be a double data type, and ratioArray stores it properly as a double.
However, idealArray does not. It stores the data in the array positions as integers. I want to know if there's something I missed, something that might have caused me to accidentally make the array an integer.
*I'm going to apologize, the code is really long. Also, I can't get it all to fit in a code window. I apologize.
using namespace std;
//Arraytype declarations
typedef int Birthday[365];
typedef bool Counter[365];
typedef double Ratio[365];
void ratioArray(int, Birthday, Ratio);
void idealArray(Ratio);
void outputTable();
int randomInt(int);
//Main function
int main()
{
Birthday array = {0};
Ratio vector = {0};
Ratio matrix = {0};
int seed;
int runs;
//Prompt the user for the number of times the simulation is to be run.
cout << "Hello and welcome to the Birthday Paradox Simulator. " << endl;
cout << "This program uses simulated runs to calculate and verify the paradox." << endl << endl;
cout << "Please enter the number of runs you want done. IMPORTANT, must be a positive integer." << endl;
cin >> runs;
while (runs <= 0)
{
cout << "That's an invalid value. Please enter a positive number." << endl;
cin >> runs;
}
//Prompt the user for a non-negative integer seed value
cout << "Please input a seed to be used for randomly generating numbers. It must be an integer, and non-negative." << endl;
cin >> seed;
while (seed < 0)
{
cout << "I'm sorry, that is an invalid value. Please enter a non-negative number)" << endl;
cin >> seed;
}
//Seed the srand function
srand(seed);
//Call birthdayFrequency function
birthdayFrequency(runs, array);
//Call ratioArray function
ratioArray(runs, array, vector);
//Call idealRatioArray function
idealArray(matrix);
//Testing values
cout << array[1] << endl;
cout << array[2] << endl;
cout << array[3] << endl;
cout << vector[1] << endl;
cout << vector[2] << endl;
cout << vector[3] << endl;
cout << matrix[1] << endl;
cout << matrix[2] << endl;
cout << matrix[3] << endl;
//Call outputTable function
outputTable();
return 0;
}
void birthdayFrequency(int n, Birthday number)
{
int iteration = 0;
int value;
int boundary = 364;
//For loop for n iterations
for ( int k =0 ; k < n ; k++)
{
Counter boolean = {0};
iteration = 0;
//Randomly mark birthdays until there's a duplicate using a for loop
for ( int i = 0; i < 366; i ++)
{
value = randomInt(boundary);
if (boolean[value] == 1)
break;
else
boolean[value] = 1;
number[iteration]++; //Increment the frequency array for every non-match
iteration++;
}
}
}
void ratioArray(int n, Birthday number, Ratio vectors)
{
double ratio;
//For loop for the number of runs, storing the value of ratios to the total number of runs.
for ( int i = 0 ; i < 364 ; i++)
{
ratio = (double)number[i] / n;
vectors[i] = ratio;
}
}
void idealArray(Ratio number)
{
number[0]= 1.0;
number[1] = 1.0;
//Create an ideal, theoretical probability array
for ( int n = 2; n < 364; n++)
{
number[n] = (number[n - 1]*(1- (n-1)/365));
}
}
void outputTable()
{
//Not completed yet.
}
int randomInt(int bound)
{
return static_cast<int>( rand() / (RAND_MAX + 1.0) * bound );
}

Answer 1

In this code:
for ( int n = 2; n < 364; n++)
{
number[n] = (number[n - 1]*(1- (n-1)/365));
}
n is an integer, therefore (1-(n-1)/365)) will evaluate to an integer value, since all values in the expression are integers. Also, an integer multiplied by an integer will produce an integer. Since you start off setting number[1] to 1.0, and each element is calculated by multiplying the previous element by an integer amount, all subsequent values will be integer amounts (although stored as doubles).
Change your code to use doubles for the calculation:
for ( int n = 2; n < 364; n++)
{
number[n] = (number[n - 1]*(1.0-((double)n-1.0)/365.0));
}