注意矩阵相乘需要三重循环来计算。

#include <iostream>
#include <algorithm>

using namespace std;

const int N = 110;

int n, m, p;
int A[N][N], B[N][N];

int main()
{
    cin >> n >> m;
    for (int i = 0; i < n; i ++ )
        for (int j = 0; j < m; j ++ )
            scanf("%d", &A[i][j]);          //读入数组A

    cin >> p;
    for (int i = 0; i < m; i ++ )
        for (int j = 0; j < p; j ++ )
            scanf("%d", &B[i][j]);          //读入数组B

    for (int i = 0; i < n; i ++ )
    {
        for (int j = 0; j < p; j ++ )
        {
            int res = 0;
            for (int k = 0; k < m; k ++ )
            {
                res += A[i][k] * B[k][j];   //三重循环输出结果
            }
            cout << res << ' ';
        }
        cout << endl;
    }

    return 0;
}