Language: C++

#include<iostream>
#include<vector>

using namespace std;

void makeMatrix(int row,int line,int* matrix)
{
  int value;
  for(int i=0;i<row;i++)
  {
    for(int j=0;j<line;j++)
    {
      cin >> value;
      matrix[i][j]=value;
    }
  }
}

void calcMatrix(int* a, int* b, int* c)
{
  int value;
  for(int i=0;i<a.size();i++)
  {
    for(int j=0;j<b[0].size();j++)
    {
      value=0;
      for(int k=0;k<b.size();k++)
      {
        value+=a[i][k]*b[k][j];
      }
      c[i][j]=value;
    }
  }
}

int main(int argc, char* argv[])
{
  int n,m,l;
  cin >> n >> m >> l;
  int matrix1[n][m];
  int matrix2[m][l];
  int matrix3[n][l];
  makeMatrix(n,m,matrix1);
  makeMatrix(m,l,matrix2);
  calcMatrix(matrix1,matrix2,matrix3);
  for (int i=0;i<matrix3.size();i++)
  {
    for(int j=0;j<matrix3[i].size();j++)
    {
      cout << matrix3[i][j];
      if(j!=matrix3[i].size()-1)cout << " ";
    }
    cout << endl;
  }
}

Compiler output:
a.cc: In function 'void makeMatrix(int, int, int*)':
a.cc:14:16: error: invalid types 'int[int]' for array subscript
   14 |       matrix[i][j]=value;
      |                ^
a.cc: In function 'void calcMatrix(int*, int*, int*)':
a.cc:22:19: error: request for member 'size' in 'a', which is of non-class type 'int*'
   22 |   for(int i=0;i<a.size();i++)
      |                   ^~~~
a.cc:24:24: error: request for member 'size' in '* b', which is of non-class type 'int'
   24 |     for(int j=0;j<b[0].size();j++)
      |                        ^~~~
a.cc:27:23: error: request for member 'size' in 'b', which is of non-class type 'int*'
   27 |       for(int k=0;k<b.size();k++)
      |                       ^~~~
a.cc:29:20: error: invalid types 'int[int]' for array subscript
   29 |         value+=a[i][k]*b[k][j];
      |                    ^
a.cc:29:28: error: invalid types 'int[int]' for array subscript
   29 |         value+=a[i][k]*b[k][j];
      |                            ^
a.cc:31:11: error: invalid types 'int[int]' for array subscript
   31 |       c[i][j]=value;
      |           ^
a.cc: In function 'int main(int, char**)':
a.cc:43:18: error: cannot convert 'int (*)[m]' to 'int*'
   43 |   makeMatrix(n,m,matrix1);
      |                  ^~~~~~~
      |                  |
      |                  int (*)[m]
a.cc:6:39: note:   initializing argument 3 of 'void makeMatrix(int, int, int*)'
    6 | void makeMatrix(int row,int line,int* matrix)
      |                                  ~~~~~^~~~~~
a.cc:44:18: error: cannot convert 'int (*)[l]' to 'int*'
   44 |   makeMatrix(m,l,matrix2);
      |                  ^~~~~~~
      |                  |
      |                  int (*)[l]
a.cc:6:39: note:   initializing argument 3 of 'void makeMatrix(int, int, int*)'
    6 | void makeMatrix(int row,int line,int* matrix)
      |                                  ~~~~~^~~~~~
a.cc:45:14: error: cannot convert 'int (*)[m]' to 'int*'
   45 |   calcMatrix(matrix1,matrix2,matrix3);
      |              ^~~~~~~
      |              |
      |              int (*)[m]
a.cc:19:22: note:   initializing argument 1 of 'void calcMatrix(int*, int*, int*)'
   19 | void calcMatrix(int* a, int* b, int* c)
      |                 ~~~~~^
a.cc:46:26: error: request for member 'size' in 'matrix3', which is of non-class type 'int [n][l]'
   46 |   for (int i=0;i<matrix3.size();i++)
      |                          ^~~~
a.cc:48:30: error: request for member 'size' in 'matrix3[i]', which is of non-class type 'int [l]'
   48 |     for(int j=0;j<matrix3[i].size();j++)
      |                              ^~~~
a.cc:51:24: error: request for member 'size' in 'matrix3[i]', which is of non-class type 'int [l]'
   51 |       if(j!=matrix3[i].size()-1)cout << " ";
      |                        ^~~~