How would I write this java code into ruby:
String[] [] Score = new String [row] [col];
Score[rCount][cCount] = num;
I thought it would as simple as:
score=[]
score[rcount][ccount]=num
But I keep getting "undefined method `[]=' for nil:NilClass (NoMethodError)"
Sorry, I don't know java, but have a look at the class methods Array#new and Array::[], and the instance methods Array#[]= and Array#[]. Here are some examples that should answer your question (and other questions that may be sparked, hopefully):
Array.new #=> []
[] #=> [] # shorthand for above
a = Array.new(5) { [] } #=> [[], [], [], [], []]
a[0][0] = 2
a #=> [[2], [], [], [], []]
a[3][2] = 4
a #=> [[2], [], [], [nil, nil, 4], []]
a[1] << 1
a #=> [[2], [1], [], [nil, nil, 4], []]
a[1] << 2
a #=> [[2], [1, 2], [], [nil, nil, 4], []]
a[1] << 3 << 4
a #=> [[2], [1, 2, 3, 4], [], [nil, nil, 4], []]
a[2] << [4,5]
a #=> [[2], [1, 2, 3, 4], [[4, 5]], [nil, nil, 4], []]
a[4].concat([4,5])
a #=> [[2], [1, 2, 3, 4], [[4, 5]], [nil, nil, 4], [4, 5]]
a = Array.new(3) { Array.new(3) }
#=> [[nil, nil, nil], [nil, nil, nil], [nil, nil, nil]]
a[1][2] = 4
a #=> [[nil, nil, nil], [nil, nil, 4], [nil, nil, nil]]
We could also write the default as a second argument:
a = Array.new(3,[]) #=> [[], [], []]
but that can be problematic:
a[0][0] = 'cat'
a #=> [["cat"], ["cat"], ["cat"]]
as is:
a = Array.new(3,Array.new(2)) #=> [[], [], []]
#=> [[nil, nil], [nil, nil], [nil, nil]]
a[0][0] = 'cat'
a #=> [["cat", nil], ["cat", nil], ["cat", nil]]
since each element of a is the same array.
Note that Ruby provides a convenience for writing certain methods that is commonly referred to as "syntactic sugar". If, for example, you write a = [1,2,3], Ruby will interpret that as a = Array.[](1,2,3) (and you could write it that way), the class method being Array::[]. Similarly, if a equals [1,2,3], a[1] = 'cat' is decoded as a.[]=(1, 'cat') and a[1] #=> 'cat' is a.[](1). Similarly, h = {} translates to h = Hash.new and so on.
Note that Ruby does not have a concept of "multidimensional arrays". For more on that you may wish to see a comment a left on this question.
Firstly, ruby programmers use snake case. Capital letter is using for class names.
Secondly, your problem happens just because
score[rcount] == nil # true
If you want to have an access to second dimension elements you need to initialize line as array:
score[rcount] = []
Now you can set second dimension element
score[rcount][ccount] = num
arrthat permitsarr[row][col] = 3to set a value andarr[row][col]to return a value.