C / C++ / MFC

Debug Assertion Failed!

I developed an exe,which would exports some pure C APIs for plugin dlls.

the code for the main exe is something like bellow:

class CA{};
class CB{};
class CC{};

class CCore
{
private:
CA* m_pCA;
CB* m_pCB;
CC* m_pCC;
};

void main()
{
CCore* pCore = new CCore;
while(true)
{
  pCore->DoSomething();	
}
delete pCore;
}

the code for a plugin is something like this

class CTestPlugin : public IPlugin
{
public:
virtual void Init()
{
	//do something to change class CCore's behavior;maybe CA,CB,CC
}
virtual void UnInit()
{
}
};

I do not want to expose the pCore pointer or any other pointers from main exe to any plugin. so I need pure c style apis.
any ideas?thank you.

#include <stdio.h>

//      Function Declarations

int main (void)
{
//      Local Declarations
        int  score1, score2, score3;
        char grade;
		int temp = 0;
		

//      Statements
        printf("Enter the test score (0-100): ");
        scanf ("%d", &score1);
		printf("Enter the test score (0-100): ");
        scanf ("%d", &score2);
		printf("Enter the test score (0-100): ");
        scanf ("%d", &score3);
		
        
        printf("The grade is: %c\n", score1, score2, score3);

        return 0;
}       // main

/*      =================== scoreToGrade ===================
        This function calculates letter grade for a score.
           Pre   the parameter score
           Post  returns the grade
*/

//      Local Declarations
int temp = 0;
{        
		temp = (score1+score2+score3)/3;

//      Statements
        if (score >= 90)
           grade = 'A';
        else
                if (score >= 80)
                        grade = 'B';
                else
                        if (score >= 70)
                                grade = 'C';
                        else
                                if (score >= 60)
                                        grade = 'D';
                                else
                                        grade = 'F';

   char grade;
 
//      Statements
        if (score >= 90)
           grade = 'A';
        else
                if (score >= 80)
                        grade = 'B';
                else
                        if (score >= 70)
                                grade = 'C';
                        else
                                if (score >= 60)
                                        grade = 'D';
                                else
                                        grade = 'F';
        return grade;
}       // scoreToGrade

struct IRender
{
    virtual void render() = 0;
}

class Sprite : public IRender
{
public:
    void render() override
    {
        //code goes here
    }
}