Basic usage of two-dimensional array

= = = = = Two dimensional array （ Yang hui triangle ） = = = = = =

One 、 Definition ：
1、 data type [ ][ ] Array name = new data type [ ] [ ]
2、 data type [ ][ ] Array name = { { },{ },{ },…,{ } ;

Two 、 The array length of a two-dimensional array represents
int[][] num = { {0,0,0} , {0,0,1,} , {0,2,0} , {0,0,0,} };

1、 Get the length of one-dimensional array ：num[ xx ].length
example ： num[ 0 ].length = 3
num[ 3 ].length = 3
2、 Get the length of the two-dimensional array ：
num.length = 4

Two 、 Realization of Yang Hui triangle
Ideas ： By observing the law of Yang Hui triangle ：
1、 The first and last numbers in each line are 1
2、 The first 1 That's ok 1 Elements , The first n That's ok n Elements
3、 Start with the third line , Every element = The upper row of elements + The previous element of the above line
It is represented by a two-dimensional array as follows ：
a[ i ] [ j ] = a[ i-1 ] [ j-1 ] + a[ i-1 ] [ j ]
So it can be realized by two-dimensional array , The code is as follows ：

import java.util.Scanner;
public class ArrayYangHui{
	public static void main(String[] args) {
	 	Scanner myScanner = new Scanner(System.in);

	System.out.println(" Please enter the number of rows of Yang Hui triangle ");
		int num = myScanner.nextInt();
		int arr[][] = new int[num][];
		for(int i = 0 ; i < arr.length ; i++){
			arr[i] = new int[i+1];// Make room for every one-dimensional array 
				
				for( int j = 0 ; j < arr[i].length ; j++ ){
					
					if(j == 0 || j == arr[i].length - 1){

					arr[i][j] = 1;// The first element and the last element are set to  1
						}else{

						arr[i][j] = arr[i-1][j-1] + arr[i-1][j];
						// The law of Yang Hui triangle 

						}
						System.out.print(arr[i][j]+" ");// Output each line of elements 
				}

				System.out.println();// Wrap each line of elements 

		}
	


	}
}