Geometric shape solver menu -trying to find variables that will let me input numbers for choices with only using basic if else statement

#include <stdio.h>

enum
{
  eRectangle = 1,
  eSquare,
  eTriangle,
  eCircle,
  eParallel,
  eEllipse
};

void solve_rectangle();
void solve_square();


int main ()
{
  int choice;
  printf ("Please Enter choice of Shape: ");
  printf ("\n1. Rectangle");
  printf ("\n2. Square");
  printf ("\n3. Triangle");
  printf ("\n4. Circle");
  printf ("\n5. Parallelogram");
  printf ("\n6. Ellipse \n");
  scanf ("%d", &choice);

  switch ( choice )
  {
  case eRectangle:
    solve_rectangle();
    break;
  case eSquare:
    solve_square();
    break;
  //...
  default:
    break;
  }
  return 0;
}

void solve_rectangle()
{
  int length, width;
  int area, perimeter;
  printf("Input length: ");
  scanf ("%d" , &length);
  printf("Input width: ");
  scanf ("%d" , &width);
  area = (length * width);
  perimeter = 2 * (length + width);
  printf ("Area of the Rectangle = %d \n" , area);
  printf ("Perimeter of the Rectangle = %d \n" , perimeter);
}

void solve_square()
{
  int length;
  int area, perimeter;
  printf("Input length: ");
  scanf ("%d" , &length);
  area = length * length;
  perimeter = 4 * length;
  printf ("Area of the Square = %d \n" , area);
  printf ("Perimeter of the Square = %d \n" , perimeter);
}

class Shape {
  int area;
  int perimeter;
 
  void print();
  virtual void compute() = 0;
  virtual void askData() = 0;
};

class Rectangle: Shape {
  // override functions
  void compute() {
  // your task
  }

}

const enum SharpForm 
  { SH_NONE, SH_RECTANGLE, SH_SQUARE, SH_TRIANGLE, SH_CIRCLE, 
    SH_PARALLEL, SH_ELLIPSE, SH_SHARPCOUNT};

int ShowMenue() {
    int sel = 0;
    cout << "\nPlease Enter choice of Shape: \n";
    cout << "1. Rectangle\n";
    cout << "2. Square\n";
    cout << "3. Triangle\n";
    cout << "4. Circle\n";
    cout << "5. Parallelogram\n";
    cout << "6. Ellipse\n";
    cout << "99. Exit\n";
    cin >> sel;
    return sel;
};

class Shape {
public:
	Shape():area(0), perimeter(0) {}
	void SetArea(int x) { area = x; }
	void SetPerimeter(int x) { perimeter = x; }
	int GetArea() { return area; }
	int GetPerimeter() { return perimeter; }
	virtual void AskData() = 0;
	virtual void PrintResult() = 0;
private:
	virtual void compute() = 0;
	int area;       // 
	int perimeter;  // 
};

class Rectangle : public Shape {
public:
	Rectangle():length(0), width(0) {};
	// override functions
	void AskData() override;
	void PrintResult() override;
private:
	void compute() override;
	int length, width;
};

void Rectangle::AskData() {
	cout << "Input length: ";
	cin >> length;
	cout << "Input width: ";
	cin >> width;
	compute();
};

void Rectangle::compute() {...}
void Rectangle::PrintResult() {...}

// class Square:Shape { ... }

int main()
{
    int choice = 0;
    do {
        choice = ShowMenue();

        // case not allowed, use if else
        if (choice == SH_RECTANGLE) {
            Rectangle r;
            r.AskData();
            r.PrintResult();
            }
        // else if(coice == SH_SQUARE,
        // else if(coice == SH_TRIANGLE,
        // else if(coice == SH_CIRCLE,
        // else if(coice == SH_PARALLEL,
        // else if(coice == SH_ELLIPSE};
    } while (choice != 99);

    return 0;
}