error: expected expression before ‘class_t’

This error message typically occurs when you try to use a class or struct variable before it has been declared or defined. To fix this error, make sure that you have declared or defined the class or struct variable before you use it in your code.

For example, if you have a class called "MyClass" and you want to create a variable of this class called "myObj", you need to make sure that you have declared the class before creating the variable.

Here's an example of how to declare the "MyClass" class and create a "myObj" variable:

class MyClass {
  // class definition here
};

int main() {
  MyClass myObj; // create a variable of type MyClass
  // rest of the code here
  return 0;
}

Make sure that you have included any necessary header files and that your syntax is correct.