1. Lecture 4
2d Arrays
CSE 1322
4/26/2018

2. 2d arrays
Working with 2D arrays is similar to 1D arrays.  But realize you need to specify two dimensional sizes and any time you access an element, you need to specify both indices.
4/26/2018

3. CREATE array nums [size_1][size_2]
define a 2D array
CREATE array nums [size_1][size_2]
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4. C# define a 2D array
<type>[ , ]<name> = new<type>[<size_1>,<size_2>];
For example:
int[ , ] grid = new int [10,20];
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5. Java define a 2D array
<type>[ , ]<name> = new<type>[<size_1>][<size_2>];
For example:
int[ ][ ] grid = new int [10][20];
4/26/2018

6. Working with 2D arrays
usually involves nested loops like this using a array called grid:
FOR each element in a row
FOR each element in a column     grid[row][col] = col * row;
4/26/2018

7. Working with 2D arrays
usually involves nested loops like this in java:
for(int row=0; row < 10; row++)   for(int col=0; col < 20; col++)     grid[row][col] = col * row;
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8. Working with 2D arrays usually involves nested loops like this in C#:
for(int row=0; row < 10; row++)   for(int col=0; col < 20; col++)     grid[row,col] = col * row;
4/26/2018

9. What is generated? Java: C#
int[,] grid = new int[10, 20]; for (int r = 0; r< 10;r++) for (int c = 0; c < 20; c++) grid[r, c] = c* r;
int[][] grid = new int[10][20]; for (int r = 0; r< 10;r++) for (int c = 0; c < 20; c++) grid[r][c] = c* r;
4/26/2018

10. multi-dimension arrays
CREATE array nums [size_1][size_2][size_3]
Use nested loops, one for each dimension to traverse the array
FOR each number in the row
FOR each number in the column
FOR each number in the third dimension
do some processing
ENDFOR
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11. C# multi-dimension arrays
int[,,] nums= new int [5,6,7];
3 nested loops using GetLength(0), GetLength(1) and GetLength(2)
for(int i=0; i<nums.GetLength(0);i++) {
for (int j=0; j< nums.GetLength(1);j++)
for(int k=0; k<nums.GetLength(2);k++)
// do some processing }
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12. C# multi-dimension arrays
int[,,] nums= new int [5,6,7]; Or use a foreach loop as long as you aren’t changing the contents of the array foreach ( int i in nums) {. . .} public static int findLargest(int[,,]n) { int max = n[0,0,0]; foreach (int j in n) { if( j > max) max = j; } return max; }
4/26/2018

13. Java multi-dimension arrays
int[][][] nums= new int [5][6][7];
3 nested loops using nums.length, nums[0].length and nums[0][0].length
for(int i=0; i<nums.length;i++) {
for (int j=0; j< nums[0].length;j++)
for(int k=0; k<nums[0][0].length;k++)
// do some processing }
4/26/2018

14. Java multi-dimension arrays
int[][][] nums= new int [5][6][7];
Use the enhanced for loop/for each loop on each subarray structure, as long as you aren’t changing the contents of the array
public static int findLargest3(int[][][]n) { int max = n[0][0][0]; for ( int [][] e : n ) for ( int [] d : e ) for ( int i : d ) { if( i > max) max = i; } return max; }
4/26/2018