C language - the use of two-dimensional arrays

Two-dimensional array

1. Application scenarios

For example, to develop a backgammon game, the board needs to be represented by a two-dimensional array

2. The use of two-dimensional arrays

快速入门案例：
请用二维数组输出如下图形
0 0 0 0 0 0
0 0 1 0 0 0
0 2 0 3 0 0
0 0 0 0 0 0

Usage 1:

语法: 类型 数组名[大小][大小];
2) 比如: int a[2][3];
3) 使用演示
4) 二维数组在内存的存在形式，各个元素的地址是连续分布的,即在
前一个元素基础上+4

Usage 2:

定义 类型 数组名[大小][大小] = {
   
   {值1,值2..},{值1,值2..},{值1,值2..}}; 
或者 类型 数组名[大小][大小] = { 值1,值2,值3,值4,值5,值6 ..};

3. Traversal of two-dimensional arrays

Case 1:

Please use a flexible way to traverse the following arrays:

int map[3][3] = { {0,0,1},{1,1,1},{1,1,3}};

Case 2:

int arr[3][2]={ {4,6},{1,4},{-2,8}};

Traverse the two-dimensional array and get the sum?

Case 3:

Define a two-dimensional array to save the results of three classes and five students in each class.

And find the average score of each class, and the average score of all classes

#include <stdio.h>
int main(){
    
    
	//定义二维数组，用于保存三个班，每个班五名同学成绩，
	//并求出每个班级平均分、以及所有班级平均分【 数据要求从控制台输入 】
	//1.创建一个score[3][5]
	double score[3][5];
	//int rows =3,cols=5,i,j;
	//更灵活的处理方式
	int rows, cols, i, j; 
    rows = sizeof(score) / sizeof(score[0]);
    cols = sizeof(score[0])/sizeof(double);
	double totalScore = 0.0,classTotalScore = 0.0;
	for(i=0;i<rows;i++){
    
    
		for(j=0;j<cols;j++){
    
    
			score[i][j]=0.0;//赋0.0，初始化
		}
	}
	
	//2.遍历，给每个学生输入成绩
	for (i = 0; i < rows; i++ ) {
    
    
		for (j = 0; j < cols ; j++ ) {
    
    
			printf("请输入第 %d 个班的  第 %d 个 学生的成绩", i + 1, j + 1);
			scanf("%lf", &score[i][j]);
		}
	}
	//getchar();
	//3.显示下成绩情况
	for (i = 0; i < rows; i++ ) {
    
    
		for (j = 0; j < cols ; j++ ) {
    
    
			printf("%.2f ",score[i][j]);
		}
		printf("\n");
	}
	//4.统计各个班的总成绩，和所有学生的总成绩
	for (i = 0; i < rows; i++ ) {
    
    
		classTotalScore = 0.0; // 每次清0 
		for (j = 0; j < cols ; j++ ) {
    
    
			classTotalScore += score[i][j]; //累计每个班的总成绩
		}
		printf("\n第 %d 个班的平均成绩是 %.2f" , i+1,  classTotalScore/cols );
		totalScore += classTotalScore; //将该班级的总分，累计到 totalScore
	}
	printf("\n所有学生总成绩是  %.2f 平均成绩 %.2f" ,  totalScore, totalScore/(rows * cols));
	getchar();
	getchar();
 
}

4. Two-dimensional array experiment details and precautions

(1) You can only assign values ​​to some elements, and the unassigned elements automatically take the "zero" value

(2) If all elements are assigned, the length of the first dimension may not be given.

int a[3][3] = {1, 2, 3, 4, 5, 6, 7, 8, 9}; 
可以写为：
int a[][3] = {1, 2, 3, 4, 5, 6, 7, 8, 9};

(3) A two-dimensional array can be regarded as a nested one-dimensional array; if each element of an array is an
array, then it is a two-dimensional array.

二维数组a[3][4]可看成三个一维数组，它们的数组名分别a[0],a[1],a[2]。
这三个一维数组都有 4 个元素，如，一维数组 a[0] 的元素为 a[0][0]、a[0][1]、a[0][2]、a[0][3]