So far all these arrays have been onedimensional. That is, a single number could locate any value in the array. However sometimes data is naturally represented by more than one number. For instance a position on the earth requires a latitude and a longitude.
The most common kind of multidimensional array is the twodimensional array. If you think of a onedimensional array as a column of values, you can think of a twodimensional array as a table of values like this
c0 
c1 
c2 
c3 

r0 
0 
1 
2 
3 
r1 
1 
2 
3 
4 
r2 
2 
3 
4 
5 
r3 
3 
4 
5 
6 
r4 
4 
5 
6 
7 
Here we have an array with five rows and four columns. It has twenty total elements. However we say it has dimension five by four, not dimension twenty. This array is not the same as a four by five array like this one:
c0 
c1 
c2 
c3 
c4 

r0 
0 
1 
2 
3 
4 
r1 
1 
2 
3 
4 
5 
r2 
2 
3 
4 
5 
6 
r3 
3 
4 
5 
6 
7 
We need to use two numbers to identify a position in a
twodimensional array. These are the element's row and column
positions. For instance if the above array is called J
then J[0][0]
is 0, J[0][1]
is 1,
J[0][2]
is 2, J[0][3]
is 3,
J[1][0]
is 1, and so on.
Here's how the elements in a four by five array called
M
are referred to:
M[0][0] 
M[0][1] 
M[0][2] 
M[0][3] 
M[0][4] 
M[1][0] 
M[1][1] 
M[1][2] 
M[1][3] 
M[1][4] 
M[2][0] 
M[2][1] 
M[2][2] 
M[2][3] 
M[2][4] 
M[3][0] 
M[3][1] 
M[3][2] 
M[3][3] 
M[3][4] 