/in/foo.cc:3:6: error: 'product' has not been declared
 void product::init_Arryc()
      ^~~~~~~
/in/foo.cc: In function 'void init_Arryc()':
/in/foo.cc:5:6: error: 'c' was not declared in this scope
      c[n][n];
      ^
/in/foo.cc:5:8: error: 'n' was not declared in this scope
      c[n][n];
        ^
/in/foo.cc:9:19: error: 'num' was not declared in this scope
         c[i][i] = num[i];
                   ^~~