C++ Virtual Galton Board - c++

Question

I have gotten this far in creating my Galton Board but fail to understand how to fix my code in regards to j and columns[j] not being in the main scope. I understand I have not declared them in the main function but not sure how to properly do so to obtain my results.
How do I get this fixed so that it outputs what my intentions are?
My intentions are simply when the code runs to output my data like so:
The number of marbles in slot 0 is 2.
The number of marbles in slot 1 is 4.
and so forth up to 7.
Here is the code I have:
#include <iostream>
#include <ctime>
using namespace std;
//Decide a L or R direction at random
char dropMarble()
{
//If 1 then L
if(rand() % 2)
{
return 'L';
}
//If 2 then R
else
{
return 'R';
}
}
void dropMarble(int columns[], int cols)
{
int i = 0, j = 0;
char LorR;
while((i + j) != cols)
{
LorR = dropMarble();
if(LorR == 'R')
{
//Marble goes right
++j;
}
else
{
//Marble goes left
++i;
}
}
cout << endl;
//Increment the count of marbles in the columns
++columns[j];
}
void printColumns(int columns[], int cols)
{
for(int i = 0; i< cols; ++i)
{
cout << columns[i] << "";
}
cout << endl;
}
int main()
{
srand(time(NULL));
int numberOfMarbles;
int numberOfColumns = 8;
int slots[numberOfColumns];
//Initialize the count of marbles in the columns to zero
for(int i = 1; i <= numberOfColumns; ++i)
{
slots[i] = 0;
}
cout << "Enter the number of marbles to drop: " << endl;
cin >> numberOfMarbles;
for(int i = 1; i <= numberOfMarbles; ++i)
{
cout << "The number of marbles in slot " << j << " is " << columns[j]
<< endl;
dropMarble(slots, numberOfMarbles);
printColumns(slots, numberOfMarbles);
}
return 0;
}

Answer 1

Not very sure what you want to achieve but you can try rewriting 2nd for loop like this -
for(int j = 0; j <= numberOfColumns; ++j) {
cout << "The number of marbles in slot " << j << " is " << slots[j]
<< endl;
dropMarble(slots, numberOfColumns);
printColumns(slots, numberOfColumns);
}

Answer 2

Is this what you're trying to do?
#include <iostream>
#include <ctime>
#include <vector>
using namespace std;
//Decide a L or R direction at random
bool dropMarble()
{
if(rand() % 2)
{
return false;
}
else
{
return true;
}
}
void dropMarble(vector<int> &columns, int cols)
{
int i = 0, j = 0;
bool GoneRight=true;
while((i + j) != cols)
{
GoneRight = dropMarble();
if(GoneRight)
{
//Marble goes right
++j;
}
else
{
//Marble goes left
// i is height small i is high, large i is low
++i;
}
}
//Increment the count of marbles in the columns
++columns[j];
}
void printColumns(vector<int> &columns, int cols)
{
for(int i = 0; i< cols; ++i)
{
cout << columns[i] << "";
}
cout << endl;
}
int main()
{
srand(time(NULL));
int numberOfMarbles;
int numberOfColumns = 8;
vector<int> slots;
slots.resize(8);
// int columns[numberOfColumns];
//Initialize the count of marbles in the columns to zero
for(int i = 1; i <= numberOfColumns; ++i)
{
slots[i] = 0;
}
cout << "Enter the number of marbles to drop: " << endl;
cin >> numberOfMarbles;
for(int i = 1; i <= numberOfMarbles; ++i)
{
dropMarble(slots, numberOfColumns);
}
for(int j = 0; j<numberOfColumns;++j){
cout << "The number of marbles in slot " << j << " is " << slots[j]
<< endl;
}
printColumns(slots, numberOfColumns);
return 0;
}
With a 1000 marbles:
The number of marbles in slot 0 is 7
The number of marbles in slot 1 is 30
The number of marbles in slot 2 is 100
The number of marbles in slot 3 is 213
The number of marbles in slot 4 is 262
The number of marbles in slot 5 is 225
The number of marbles in slot 6 is 122
The number of marbles in slot 7 is 34
73010021326322512234
Interesting idea. The key change really is to pass by reference a vector. You don't have to use a vector, you could parse an array via a pointer that would work also.
The other thing was to change the marble printing logic so it's in its own loop, and also to parse the number of columns rather than the number of marbles to your other functions.