Iterating through an array of objects C++

There are several mistakes in your given code snippet. You can correct them as i have shown below. I have added comments wherever i have made changes.

MyClass.h

#ifndef MYCLASS_H
#define MYCLASS_H
// MyClass.h
class MyClass
{
/* class definitions */
public:
MyClass() = default;
};

extern MyClass object[20]; //declare object as an array 

#endif

MyClass.cpp

// MyClass.cpp
#include "MyClass.h"

/* Constructors, Destructors, Functions */

main.cpp

#include <iostream>
#include "MyClass.h"

 MyClass object[20];    // define object here instead of inside main()
void reload_objects();  // reload_objects() doesnt take any argument by looking at its call and definiton

int main()
{
  // MyClass object[20]; //don't define object here
   reload_objects();
}

void reload_objects()  //you had a semicolon here so i removed it
{
   for (int i = 0; i < 20; i++){
      object[i].setProperties(/*args*/);
      ;
   }
}

Also don't forget to add the definition and declaration of your other member functions like setProperties in the above example for it to work. These are some of the changes that i made:

1. You should declare object as an array of size 20 inside MyClass.h.
2. Define object outside of main() inside main.cpp as i did in my example.
3. Declare the function reload_objects() with no arguments in main.cpp.