/in/foo.cc: In function 'int main()':
/in/foo.cc:7:13: error: declaration of 'c' as multidimensional array must have bounds for all dimensions except the first
    7 |         int c[][];
      |             ^
/in/foo.cc:11:17: error: 'c' was not declared in this scope
   11 |                 c[i][j] += a[i][k]*b[k][j];
      |                 ^
/in/foo.cc:17:21: error: 'c' was not declared in this scope
   17 |             cout << c[i][j];
      |                     ^