二维数组

数组里面还是， 类似数学中的矩阵

#include <iostream>
using namespace std;
int main(){
    //    int arr[] = {1, 2, 3}
    // 定义一个二位数组
    const int M = 3, N =4 ;
    int  arr[M][N] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12};
    // 遍历
    for (int i = 0; i < M; ++i) {
        for (int j = 0; j < N; ++j) {
            cout<<arr[i][j]<<"\t"; //第 i 行 第 j 列
        }
        cout<<endl;
    }

}

二维数组的定义方式

1. 数据类型 数组名[行数][列数];
2. 数据类型 数组名[行数][列数] = {{数据1, 数据2...}, ..... {数据n, 数据n+1}....};
3. 数据类型 数组名[行数][列数] = {数据1, 数据2, ......};
4. 数据类型 数组名[][列数] = {数据1, 数据2, ......};

可以省略行, 不可以省略列

#include <iostream>

using namespace std;

int main() {
//    1. 数据类型 数组名[行数][列数];
    int arr[2][3];
    // 没有赋值时, 数组中的变量是不确定的
    for (int i = 0; i < 2 ; ++i) {
        for (int j = 0; j < 3; ++j) {
            cout<<arr[i][j]<<"\t"; //第 i 行 第 j 列
        }
        cout<<endl;
    }
    // 赋值
    arr[0][0] = 1;
    arr[0][1] = 2;
    arr[0][2] = 3;
    arr[1][0] = 4;
    arr[1][1] = 5;
    arr[1][2] = 6;
    cout<<"===================================="<<endl;
    for (int i = 0; i < 2 ; ++i) {
        for (int j = 0; j < 3; ++j) {
            cout<<arr[i][j]<<"\t"; //第 i 行 第 j 列
        }
        cout<<endl;
    }
//    2. 数据类型 数组名[行数][列数] = {{数据1, 数据2...}, ..... {数据n, 数据n+1}....};
    cout<<"===================================="<<endl;
    int arr2[2][3] = {{1, 2, 3},  {4, 5, 6}};
    for (int i = 0; i < 2 ; ++i) {
        for (int j = 0; j < 3; ++j) {
            cout<<arr2[i][j]<<"\t"; //第 i 行 第 j 列
        }
        cout<<endl;
    }
//    3. 数据类型 数组名[行数][列数] = {数据1, 数据2, ......};
    cout<<"===================================="<<endl;
    int arr3[2][3] = {1, 2, 3, 4, 5, 6};
    for (int i = 0; i < 2 ; ++i) {
        for (int j = 0; j < 3; ++j) {
            cout<<arr3[i][j]<<"\t"; //第 i 行 第 j 列
        }
        cout<<endl;
    }
//    4. 数据类型 数组名[][列数] = {数据1, 数据2, ......};
    cout<<"===================================="<<endl;
    int arr4[][3] = {1, 2, 3, 4, 5, 6};
    for (int i = 0; i < 2 ; ++i) {
        for (int j = 0; j < 3; ++j) {
            cout<<arr4[i][j]<<"\t"; //第 i 行 第 j 列
        }
        cout<<endl;
    }
}

⼆维数组数组名

• 查看⼆维数组所占内存空间
• 获取⼆维数组⾸地址

image

#include <iostream>

using namespace std;

int main() {
    // 计算三名同学的总成绩
    int scores[][3] = {{100, 100, 100}, {90, 30, 100}, {60, 70, 80}};
    string names[] = {"zhangsan", "lisi", "wangwu"};

    for (int i = 0; i < 3; ++i) {
        int sum = 0;
        for (int j = 0; j < 3; ++j) {
            sum += scores[i][j];
        }
        cout<<names[i] <<"  total score  = "<<sum<<endl; //
        cout<<names[i] <<"  mean score  = "<<sum/3.0<<endl; //
    }

}

编写程序实现矩阵的转置操作（行变列， 列变行）

#include <iostream>

using namespace std;

int main() {
    int X[5][4]={{1, 2, 3, 4}, { 5, 6, 7, 8,}, {9, 10, 11, 12}, {13, 14, 15, 16}, {17, 18, 19, 20}};
    int XT[4][5];
    cout<< "T before ------------------------------" <<endl;
    for (int i = 0; i < 5 ; ++i) {
        for (int j = 0; j < 4; ++j) {
            cout<<X[i][j]<<"\t";
        }
        cout<<endl;
    }
    // 转置
    for (int i = 0; i < 5; ++i) {
        for (int j = 0; j < 4; ++j) {
            // 核心代码  行变列 , 列变行
            XT[j][i] = X[i][j];
        }
    }
    cout<< "T After ------------------------------" <<endl;
    for (int i = 0; i < 4 ; ++i) {
        for (int j = 0; j < 5; ++j) {
            cout<<XT[i][j]<<"\t";
        }
        cout<<endl;
    }
}

作业

统计数组a和b对应位置元素相等的个数

int a[3][4]={1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12},
   int  b[3][4]={12, 2, 3, 4, 10, 6, 7, 11, 9, 5, 8, 1};