Access an array of class in a function

You're creating an array of pointers here:

Totscore *st[MAX];

But you're passing the first element:

PrintArray(*st);

Changing your function to take a pointer to the entire array should work:

void PrintArray(Totscore **stu){ 
    for(int i=0; i< MAX; i++){
        stu[i]->Display();       
    }
}

PrintArray(st);

Few major problems leading to undefined behavior:

1. Default constructor of Student does not initialize its char array.
2. Arrays passed by value into constructors.
3. Incorrect iteration trough array. Memory layout of array of objects is different from array of pointers to objects.

Well, there is also a memory leak, many unnecessary operations just to initialize data. You should use constructor initialization lists instead. There is no strcpy_s function in C/C++, it is a terrible Microsoft invention. Why not to use portable strncpy instead?

Here is a bit improved code:

#include <cstring>
#include <iostream>

using namespace std;

#define MAX 5       //size of array

//Class 'Student' 
class Student
{
public:
    Student (int num = 0) : num (num)
    {
        name[0] = '\0';
    }

    Student (const char *name, int num = 0) : num (num)
    {
        strncpy (this->name, name, sizeof (this->name));
    }

    int num;
    char name[10];
};

//Class 'Lscore' extends Student (virtual)
class Lscore : virtual public Student   
{
public: 
    Lscore (int eng = 0) : eng (eng) {}
    int eng;    
};

//Class 'Nscore' extends Student (virtual)
class Nscore : virtual public Student
{
public:
    Nscore (int math = 0) : math (math) {}
    int math;   
};

//Class 'Totscore' extends Lscore, Nscore
class Totscore : public Lscore, public Nscore
{
public:
    Totscore() {}     //Constructor1
    Totscore(const char *name, int num, int eng, int math); //Constructor2
    void Display();     //Print Myself
};

//Constructor2
Totscore::Totscore(const char *name, int num, int eng, int math)
        : Student (name, num), Lscore (eng), Nscore (math)
{       
}


//Print Myself
void Totscore::Display(){
    cout<<this->num<<"  "<<this->name<<"  "
        <<this->eng<<"  "<<this->math<<"  \n";
}


//Print Array (--- Problem Part !! ---)
void PrintArray(Totscore **stu){ 
    for(int i=0; i< MAX; ++i){
        stu[i]->Display();       
    }

}

void DeleteArray(Totscore **stu){ 
    for(int i=0; i< MAX; ++i){
        delete stu[i];
    }
}

//Main Function
int main(){
    Totscore *st[MAX];      //Class Array 'st'

    st[0] = new Totscore("A",101,85,77);
    st[1] = new Totscore("B",102,90,89);
    st[2] = new Totscore("C",103,80,55);
    st[3] = new Totscore("D",104,75,85);
    st[4] = new Totscore("E",105,85,85);

    PrintArray(st);
    DeleteArray (st);
}

This code is painful to look at. A couple of tips that you can use to quickly and easily improve your code in general:

In C++, favor const over #define for constants.

#define MAX 5  // Instead of this...
const int MAX = 5;  // ...do this.

Likewise, user std::string name over char *name or char name[10]. Otherwise, you're just writting C with classes, and there's enough of that out there already, unfortunately. Don't add to the pain. :)

Learn to use the standard containers types (vector, list, set and friends) instead of bare arrays. There's no reason not to and the built-in functionality they provide is amazing! There's a learning curve, of course. But you will come out much better in the end.

If you want an array of objects you must declare the array as:

Totscore st[MAX];

And allocate Totscore objects on the stack (remove "new"). Finally, call the print function without dereferencing as:

PrintArray(st);

And your original code will work...

First, I will tell you what you need to do (without asking you to change the whole code) in order to make your code work, then explain why your code doesn't work:

Implement your printArray as:

void PrintArray(Totscore **stu){ 
    for(int i=0; i< MAX; i++){
        stu[i]->Display();     
    }
}

then call it as:

PrintArray(st);

This should work.

Now why your original code doesn't work is because you're passing the first element of array, which cannot be used to traverse the array which is declared as array of pointers. Since st is declared as array of pointers, so you need to pass the address of first element of the array, rather than the element itself, so that you can traverse through the array of pointers. Note that the type of element of the array is Totscore*, so its address will be Totscore**.

Well that is very complicated for beginners, so I would suggest a better, robust and easy alternative. Use std::vector as:

std::vector<Totscore> st;

then call .push_back() to insert elements to it:

st.push_back(Totscore("A",101,85,77));
st.push_back(Totscore("B",102,90,89));
st.push_back(Totscore("C",103,80,55));
//etc

PrintArray(st);

then implement PrintArray as:

void PrintArray(const std::vector<Totscore> & stu)
{ 
    for(size_t i=0; i< stu.size(); i++){
        stu[i].Display();     
    }
}

Now there is one more very little change you need to make in your code. Make the Display() function a const member function.

void Display() const;
               ^^^^^ //this makes the  function const!
                     //in its definition too, write const!

Done!