数组上下左右遍历的简便写法
#include <iostream>

using namespace std;

int dx[] = {-1, 0, 1, 0}, dy[] = {0, 1, 0, -1};//上右下左

int f[5][5];
int r, c;

int main(){
    int cnt = 1, r = 5, c = 5;
    for(int i = 1; i <= r; i ++){
        for(int j = 1; j <= c; j ++){
            f[i][j] = cnt ++;
        }
    }

    for(int i = 1; i <= r; i ++){
        for(int j = 1; j <= c; j ++){
            cout << f[i][j] << ' ';
        }
        cout << endl;
    }

    int x = 3, y = 3;
    for(int i = 0; i < 4; i ++){
        int a = x + dx[i], b = y + dy[i];//上下左右四个方向的坐标
        if(a >= 1 && a <= r && b >= 1 && b <= c){//判断是否越界
            cout << f[a][b] << ' ';
        }
    }

    return 0;
}
样例
矩阵如下：
1  2  3  4  5 
6  7  8  9  10 
11 12 13 14 15 
16 17 18 19 20 
21 22 23 24 25 

结果展示：
8 14 18 12          // a[3][3] = 13, 其上右下左的元素