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Multi-Dimensional Arrays
Arrays that have more than one index:
Example of differences between basic data types and arrays using
integers:
Basic integer: int a;
-- Only has one value associated with it at one time
-- Unless specified otherwise, a basic variable is passed to a
function by value
1D array: int a[SIZE]
-- Has a series of values associated with it:
a[0], a[1], a[2], ….a[SIZE-1]
2D array: int a[ROWSIZE][COLSIZE]
-- Has a series of values associated with it:
a[0][0], a[0][1], a[0][2], …a[0][COLSIZE-1], a[1][0],…
Multi-D array: int a[SIZE][SIZE][SIZE]…
Arrays are almost always passed by reference
Referring to Two-Dimensional Array
Elements
Format
arrayName[ rowIndex ][ colIndex ]
2
-3 23 25
5
9
10
0
17 -13
9
8
The accessed element of the array is on Row rowIndex and Column colIndex
Both row and column indices start from 0, and must be
an integer or an integer expression.
The names of the elements in
the i-th row all have a first
suscript/index of i.
The names of the elements in
the j-th column all have a
second suscript/index of j.
Passing Two-Dimensional Arrays to
Functions
Defining the function: The function’s parameter list must
specify that a two-dimensional array will be received.
#define ROWSIZE 10
#define COLSIZE 10
Specifies the number of columns of the
array parameter, which is required.
void oneFunc( int ary[ ] [ COLSIZE ] , int rowSize, int colSize )
The number of rows of the array
parameter is NOT required.
Normally, also pass the
numbers of rows and
columns of the array
argument.
The header of
the function
Calling the function
To pass an array argument to a function, specify the
name of the array without any brackets
int anArray[ ROWSIZE ][ COLSIZE ] = {{0}};
oneFunc( anArray, ROWSIZE, COLSIZE );
 Array size usually passed to function
Two-Dimensional Arrays - An Example
Compute a multiplication table
*
1
2
3
4
5
6
7
8
9
1
1
2
3
4
5
6
7
8
9
2
2
4
6
8 10 12 14 16 18
3
3
6
9 12 15 18 21 24 27
4
4
8 12 16 20 24 28 32 36
5
5 10 15 20 25 30 35 40 45
6
6 12 18 24 30 36 42 48 54
7
7 14 21 28 35 42 49 56 63
8
8 16 24 32 40 48 56 64 72
9
9 18 27 36 45 54 63 72 81
Here is the code for the multiplication table
#include <stdio.h>
Standard input/output – printf/scanf
int main()
{
int nrows = 10, ncols = 10;
int mult_table[10][10];
int row, col;
Start main
}
Declare the number of rows/columns
Declare a 10x10 array
Declare row and column counter
printf("* 0 1 2 3 4 5 6 7 8 9\n");
Print out first line
for (row = 0; row < nrows; row++)
{
printf("%d ", row);
for (col = 0; col < ncols; col++)
{
mult_table[row][col] = row*col;
printf("%2d ", mult_table[row][col]);
}
printf("\n");
}
Start loop over the rows
Print out row number
Loop over the columns
Calculate multidimensional array
Print multidimensional array by filling
the columns fist
Start new line
Let’s go through this code segment:
printf("* 0 1 2 3 4 5 6 7 8 9\n");
for (row = 0; row < nrows; row++)
{
printf("%d ", row);
for (col = 0; col < ncols; col++)
{
mult_table[row][col] = row*col;
printf("%2d ", mult_table[row][col]);
}
printf("\n");
}
}
The print out to the screen:
This is the very 1st line
* 0 1 2 3 4 5 6 7 8 9
0 0 0 0 0 0 0 0 0 0 0
1 0 ……
This column (except for the ‘*’) comes from printing out “row”
The use of 2-D arrays in imaging
Suppose you wanted to find Waldo in the image below.
Each pixel has a “color” (which is represented by a
number) associated with it that can be stored as a 2-D
array
Can search this 2D array in order to find the correct
match with Waldo!