How I will multiply this matrix by using for loop ?

```
#include<iostream>
using namespace std;
void mat_mul_2d(int mat_out_2d[][2], int mat_in1_2d[][2], int mat_in2_2d[][2])
{
mat_out_2d[0][0]=mat_in1_2d[0][0]*mat_in2_2d[0][0]+mat_in1_2d[0][1]*mat_in2_2d[1][0];
mat_out_2d[1][1]=mat_in1_2d[0][0]*mat_in2_2d[0][1]+mat_in1_2d[0][1]*mat_in2_2d[1][1];
mat_out_2d[2][2]=mat_in1_2d[1][0]*mat_in2_2d[0][0]+mat_in1_2d[1][1]*mat_in2_2d[1][0];
mat_out_2d[3][3]=mat_in1_2d[1][0]*mat_in2_2d[0][1]+mat_in1_2d[1][1]*mat_in2_2d[1][1];
}
int main()
{
int mat_in1_2d[2][2] = {{1, 2},{3, 4}}; /
int mat_in2_2d[2][2]={{1,0},{0,1}};
int mat_out_2d[2][2]={{0},{0}};
mat_mul_2d(mat_out_2d,mat_in1_2d,mat_in2_2d);
return 0;
}
```