Double-precision Random number array

got some homework to produce a program that loads and displays double-precision random numbers with an array size of 20. i know its messy but not to good at this

#include <iostream> //required for cin, cout, endl
#include <cstdlib> //rewuired for setw(), setfill()
#include <iomanip>

using namespace std;


void printArray(int arr[]); 
void fillRandArray(int arr[]);
void fillDecimalArray(double dArr[]); 
void printDecimalArray (double dArr[]);

int main()
{

int random[21];
double decimal[21]; 
rand();

fillRandArray(random); 
fillDecimalArray(decimal);
printArray(random); 
printDecimalArray(decimal);


cin.get();
cin.get();
return 0;
}

void fillRandArray(int arr[]) 
{
for (int i = 1; i < 21; i++)
{
    arr[i] = rand() % 100 + 1;
}

}//end load of rand array

void fillDecimalArray(double dArr[ ])
{
for (double i = 1; i <21; i++)
{
    dArr[i] = static_cast<double>(rand()%100)/10;
}
}

void printArray(int arr[]) 
{
cout <<  "          5x4 Array" <<endl;
cout <<endl;

int cols = 5;

for(int i = 1; i < 21; i++)
{
    cout << setw(5) << setfill(' '); 
    cout << arr[i];
    if(i%cols == 0)
        cout << endl;
}//end print array

}//end of printArray()

void printDecimalArray (double dArr[])
{
int cols = 4;

for (double i = 1; i <21; i++)
{
    cout << setw(5) << setfill(' '); 
    int precision = 2;
    cout << dArr[i];
    cout << endl;
}
}

needs to be displayed in 4x5 table errors are ' invalid types 'double*[double]' for array subscript '