遍历就完事了 

#include<iostream>
using namespace std;
int main()
{
	int a[3][3], b[3][3], c[3][3];
	for (int i = 0; i < 3; i++) {
		for (int j = 0; j < 3; j++) {
			cin >> a[i][j];
		}
	}
	for (int i = 0; i < 3; i++) {
		for (int j = 0; j < 3; j++) {
			cin >> b[i][j];
		}
	}
	for (int i = 0; i < 3; i++) {
		for (int j = 0; j < 3; j++) {
			c[i][j] = 0;
			for (int k = 0; k < 3; k++) {
				c[i][j] += a[i][k] * b[k][j];
			}
		}
	}
	for (int i = 0; i < 3; i++) {
		for (int j = 0; j < 2; j++) {
			cout << c[i][j] << " ";
		}
		cout << c[i][2] << endl;
	}
	return 0;
}